Biology cell mcq

1. Who discovered cell in 1665?

a) Robert Hook

b) Robert Crook

c) David Thomson

d) Marie Francois

Ans. a)

2. Name an Organelle which serves as a primary packaging area for molecules that will be distributed throughout the cell?
a) Mitochondria

b) Plastids

c) Golgi apparatus

d) Vacuole

Ans. c)

3. Name the outer most boundary of the cell?

a) Plasma membrane

b) Cytoplasm

c) Nuclear membrane

d) None of the above

Ans. a)

4. Name the process in which the ingestion of material by the cells is done through the plasma membrane?

a) Egestion

b) Diffusion

c) Osmosis

d) Endocytosis

Ans. d)

5. Which among the following sentence is not correct about the organelles?
a) They are found in all Eukaryotic cells.

b) They are found in multicellular organisms.

c) They coordinate to produce the cell.

d) They are small sized and mostly internal.

Ans. b)
6. Name the process in which the passage of water goes from a region of higher concentration to a region of lower concentration through a semi permeable membrane?

a) Diffusion

b) Osmosis

c) Both a) and b)

d) Neither a) nor b)

Ans. b)

7. Name an organism which contains single chromosome and cell division occurs through fission or budding?

a) Eukaryotes

b) Prokaryotes

c) Bacteria

d) Primitive organism

Ans. b)

8. Name the process in which the membrane of a vesicle can fuse with the plasma membrane and extrude its contents to the surrounding medium?

a) Exocytosis

b) Endocytosis

c) Osmosis

d) Diffusion

Ans. a)

9. The jelly like substance present inside the cell is known as:

a) Cytoplasm

b) Ectoplasm

c) Nucleoplasm

d) None of the above

Ans. a)

10. Blue green Algae are:

a) Prokaryotes

b) Eukaryotes

c) Both a) and b)

d) Neither a) nor b)

Ans. a)

Earwax

                             Earwax


Why do we have Earwax and what is its function?

The earwax is very useful substance which keeps our ears healthy and is produced naturally in the ear. This wax is found not only in humans, but also in animals. It cleans, protects and lubricates the ears. Let us study through this article about earwax, its function etc.
Important facts about Earwax
1. The scientific name of the earwax is cerumen. It is formed in the outer part of our ear canal where there are thousands of glands. It is sticky and shiny substance. It coats the ear to moisturize it and fight against infection.
2. Earwax also prevents from dust, dirt, and insects from entering the ear.
3. It also works like a natural antibiotic, i.e. it contains anti-microbial properties. According to some researchers, cerumen contains a lysozyme antibacterial enzyme which is capable of destroying the walls of the cells of bacteria.
4. With the help of earwax, you can tell which family you belong to. People have wet or dry wax. Although, both the wax is made up of chemicals. But it depends upon the family that the wax will be wet or dry in your ear. This is detected by the gene. This gene is called ABCC11. If the gene G is replaced by gene A, then, the wax in the ear will be dry and its odour will also be different.

What is the function of Earwax in the Human Body?

Some people have dry or wet earwax. This wax is very useful and helps in keeping our ears healthy. It lubricates and protects the ear. This article deals with some important facts about earwax, its function etc.

Coronavirus

Coronaviruses (CoV) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). A novel coronavirus (nCoV) is a new strain that has not been previously identified in humans.  

Coronaviruses are zoonotic, meaning they are transmitted between animals and people.  Detailed investigations found that SARS-CoV was transmitted from civet cats to humans and MERS-CoV from dromedary camels to humans. Several known coronaviruses are circulating in animals that have not yet infected humans. 

Common signs of infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. In more severe cases, infection can cause pneumonia, severe acute respiratory syndrome, kidney failure and even death. 

Standard recommendations to prevent infection spread include regular hand washing, covering mouth and nose when coughing and sneezing, thoroughly cooking meat and eggs. Avoid close contact with anyone showing symptoms of respiratory illness such as coughing and sneezing.

Ray optics mcq

Ray optics mcq

1. The speed of light is_______ in vacuum.
   
   
   
   1. 3 x 10⁵ m/s 
   2. 3 x 10⁸ m/s 
   3. 3 x 10⁸ km/s 
   4. 3 x 10⁶ m/s 
2. The wavelength of the visible light is ________.
   
   
   
   1. 4 x 10^(-7) to 8 x 10^(-7) m 
   2. 4 x 10⁷ to 8 x 10⁷ m 
   3. 4 x 10^(-7) to 8 x 10^(-7) Å 
   4. 4 x 10⁷ to 8 x 10⁷ Å 
3. We can see objects because of_______
   
   
   
   1. reflection 
   2. refraction 
   3. transmission 
   4. diffraction
4. The image formed by a convex mirror is always________
   
   
   
   1. real 
   2. enlarged
   3. virtual and enlarged 
   4. diminished
5. As you move an object away from a convex mirror, its image becomes_____ and moves towards______
   
   
   
   1. smaller, infinity 
   2. smaller, focus
   3. enlarged, infinity 
   4. enlarged, focus
6. For a spherical mirror, ______ is true.
   
   
   
   1. f = 2R 
   2. R = 2f
   3. fR = 2 
   4. fR = 1/2
7. The mirror formula is ________.
   
   
   
   1. 1/u - 1/v = 1/f 
   2. 1/f + 1/u = 1/v
   3. f = uv/(u+v) 
   4. f = (u+v)/uv
8. For a plane mirror, magnification (m)=________
   
   
   
   1. 0 
   2. 1
   3. ± 1 
   4. ≤ 0
9. Magnification for convex mirror is ________.
   
   
   
   1. always positive 
   2. always negative
   3. sometimes positive 
   4. 1
10. The image formed by a concave lens is ________.
    
    
    
    1. always real and enlarged 
    2. always real and diminished
    3. always virtual and enlarged 
    4. always virtual and diminished
11. The lens formula is ________.
    
    
    
    1. 1/f = 1/u + 1/v 
    2. 1/f = 1/u - 1/v
    3. 1/f = 1/v - 1/u 
    4. 1/f + 1/v = u
12. 1 diopter = ________.
    
    
    
    1. 1 m 
    2. 1 m^(-1)
    3. 1 cm 
    4. 1 cm^(-1)
13. Which of the following is a true statement?
    
    
    
    1. The power of a lens is always positive. 
    2. The power of a lens is always negative.
    3. The power of a convex lens is positive. 
    4. The power of a concave lens is positive.
14. Image formed by a concave mirror is erect and enlarged.What is the position of the object?
    
    
    
    1. Between focus F and the center of curvature 
    2. At the center of curvature
    3. Beyond the center of curvature 
    4. Between pole and the focus
15. If the focal length of a spherical mirror is 40 cm, then its radius of curvature is _______ cm.
    
    
    
    1. 80 
    2. 20
    3. 10 
    4. 5
16. The velocity of light in vacuum is _______ ms^(-1)
    
    
    
    1. 3 x 10⁶ 
    2. 3 x 10⁸
    3. 3 x 10 ¹² 
    4. 3 x 10¹⁵
17. If the angle of incidence, θ_i = 0°, the angle of reflection, θ_r = ________.
    
    
    
    1. 0° 
    2. 90°
    3. 180° 
    4. 45°
18. No matter how far is the object from the mirror, the image of the object appears erect. The mirror is ________.
    
    
    
    1. concave 
    2. convex
    3. either concave or convex 
    4. none of these
19. A boy is standing at a distance of 2 m in front of a plane mirror.The distance between the boy and his image is ________ m.
    
    
    
    1. 4 
    2. 3
    3. 2 
    4. 1
20. The image formed by a concave mirror is real, inverted and of the same size as that of the object.The position of the object should be ________.
    
    
    
    1. beyond the center of curvature of mirror 
    2. between the center of curvature and the focus
    3. at the center of curvature of the mirror 
    4. at the focus
21. Which of the following has the highest refractive index?
    
    
    
    1. Glass 
    2. Water
    3. Pearl 
    4. Diamond
22. Absolute refractive index of any medium is always _______.
    
    
    
    1. 1 
    2. > 1
    3. < 1 
    4. 0
23. The image formed by a plane mirror is ______.
    
    
    
    1. real 
    2. diminished
    3. enlarged 
    4. laterally inverted
24. The incident ray passing through the focus(F) of a mirror ______ after reflection.
    
    
    
    1. passes through C 
    2. passes through F
    3. becomes parallel to the principal axis 
    4. passes through the pole
25. The incident ray passing through the center of curvature(C) of a mirror ______ after reflection.
    
    
    
    1. passes through C 
    2. passes through F
    3. passes through the pole 
    4. becomes parallel to the principal axis
26. The incident ray parallel to the principal axis of a mirror ______ after reflection.
    
    
    
    1. passes through C 
    2. passes through F
    3. passes through the pole 
    4. reverts back in the opposite direction
27. According to the sign convention, the distance of object...
    
    
    
    1. is always positive 
    2. is always negative
    3. may be positive or negative 
    4. is equal to object height
28. According to the sign convention, the distance of image...
    
    
    
    1. is always positive 
    2. is always negative
    3. may be positive or negative 
    4. is equal to image height
29. The refractive index of a denser medium with respect to a rarer medium is...
    
    
    
    1. 1 
    2. greater than 1
    3. smaller than 1 
    4. negative
30. The refractive index of a rarer medium with respect to a denser medium is...
    
    
    
    1. 1 
    2. greater than 1
    3. smaller than 1 
    4. negative
31. Total internal reflection will occur if the angle of reflection is...
    
    
    
    1. 45° 
    2. 60°
    3. 90° 
    4. 99°
32. Magnification for ______ image is always ______.
    
    
    
    1. real, positive 
    2. real, negative
    3. virtual, negative 
    4. any, negative
33. If magnification is +1.5, the image is______.
    
    
    
    1. erect
    2. diminished
    3. real
    4. inverted

ANSWERS TO MCQs:


(1) B (2) A (3) A (4) D (5) B (6) B (7) C (8) B (9) A (10) D (11) C (12) B (13) C (14) D (15) A (16) B (17) A (18) B (19) A (20) C (21) D (22) B (23) D (24) C (25) A (26) B (27) B (28) C (29) B (30) C (31) D (32) B (33) A

Optics mcq

1.   Focal length of plane mirror is

         a. At infinity

         b. Zero

         c. Negative

         d. None of these

2.   Image formed by plane mirror is

         a. Real and erect

         b. Real and inverted

         c. Virtual and erect

         d. Virtual and inverted

3.   A concave mirror gives real, inverted and same size image if the object is placed

         a. At F

         b. At infinity

         c. At C

         d. Beyond C

4.   Power of the lens is -40, its focal length is

         a. 4m

         b. -40m

         c. -0.25m

         d. -25m

5.   A concave mirror gives virtual, refract and enlarged image of the object but image of smaller size than the size of the object is

         a. At infinity

         b. Between F and C

         c. Between P and F

         d. At E

6.   In optics an object which has higher refractive index is called

         a. Optically rarer

         b. Optically denser

         c. Optical density

         d. Refractive index

7.   The optical phenomena, twinkling of stars, is due to

         a. Atmospheric reflection

         b. Total reflection

         c. Atmospheric refraction

         d. Total refraction

8.   Convex lens focus a real, point sized image at focus, the object is placed

         a. At focus

         b. Between F and 2F

         c. At infinity

         d. At 2F

9.   The unit of power of lens is

         a. Metre

         b. Centimeter

         c. Diopter

         d. M-1

10.   The radius of curvature of a mirror is 20cm the focal length is

         a. 20cm

         b. 10cm

         c. 40cm

         d. 5cm

Answers

1.   A

2.   C

3.   C

4.   C

5.   C

6.   B

7.   C

8.   C

9.   C

10. B

ELECTRICITY MCQ QUESTIONS

1.  What is the rate of flow of electric charges called?

(a)  Electric potential

(b)  electric conductance

(c)  Electric current

(d)  none of these

2.  Which of the following is the SI Unit of Electric Current?

(a)  ohm

(b)  ampere

(c)  volt

(d)  faraday

3.  Which instrument is used for measuring electric potential?

(a)  Ammeter

(b)  galvanometer

(c)  voltmeter

(d)  potentiometer

4.  When one unit electric charge moves from one point to another point in an electric circuit, then the amount of work done in joules is known as?

(a)  Electric current

(b)  electric resistance

(c)  electric conductance

(d)  potential difference

5.  The hindrance presented by material of conductor to the smooth passing of electric current is known as:

(a)  Resistance

(b)  Conductance

(c)  Inductance

(d)  None of these

6.  The resistance of a conductor is directly proportional to:

(a)  Its area of cross-section

(b)  density

(c)  melting point

(d)  length

7.  The purpose of a rheostat is:

(a)  Increase the magnitude of current only

(b)  Decrease the magnitude of current only

(c)  Increase or decrease the magnitude of current

(d)  None of these

8.  Point to be kept in mind for verification of Ohm’s Law is:

(a)  Ammeter and voltmeter should be connected in series

(b)  Ammeter should be connected in series and voltmeter in parallel

(c)  Ammeter should be connected in parallel and voltmeter in series

(d)  Ammeter and voltmeter should be connected in parallel

9.  When a 40V battery is connected across an unknown resistor there is a current of 100 mA in the circuit. Find the value of the resistance of the resister:

(a)  5000 Ω

(b)  800 Ω

(c)  0.8 Ω

(d)  none of these

10.  A battery of 6V is connected in series with resisters of 0.1 ohm , 0.15 ohm,0.2 ohm,0.25 ohm and 6 ohm. How much current would flow through the 0.3 ohm resistor?

(a)  0.895A

(b)  2.22A

(c)  1A

(d)  none of these

11.  A fuse wire is inserted in a?

(a)  . Live wire

(b)  . In the neutral wire

(c)  . In the earth wire

(d)  . May be connected in any line.

12.How the charge will flow?
(a)By heating them
(b)By applying potential difference
(c)Both
(d)None of the above

13.If length of a conductor and it’s radius is increased twice, how the resistance will change?
(a)Resistance will remain unchanged
(b)Resistance increases twice
(c)Resistance will become half
(d)Resistance will increase 4 times

14. The potential difference applied is directly proportional to current only if
(a)Always
(b)Never
(c)Sometimes
(d)When temperature is constant

15.Equivalent resistance of 4 4Ω resistances in parallel is
(a)4Ω
(b)1Ω
(c)2Ω
(d)16Ω

16. Which of the following conditions represent more resistance at constant temp?
(a)The red line
(b)The yellow line
(c)Both are equal
(d)Can’t be said

17. There is a wire of length l and cross section A. Which of the following have least Resistance?
(a)Length doubled, Area halved
(b)Length tripled, Area doubled
(c)Length halved, Area doubled
(d)The original Wire

18.On which of the following parameters specific resistance depends?
(a)Length of wire
(b)Area of wire
(c)Current passing through it
(d)Temperature

19. A resistor of length l is connected to a battery and current I is flowing through it. If it is divided into 3 parts by length, and all are having same cross sectional area are connected in series with the same battery, the current flowing through them will be?
(a)I/3
(b)3I
(c)I
(d)3I/2

20.Two resistances R1 and R2 are connected with a cell in parallel. Find the ratio of current flowing through R1to the current flowing through R2.
(a)R1:R2
(b)R2:R1
(c)1:1
Data not sufficient

21. Which of the following statement is true regarding Ammeter and Voltmeter?
(a)Ammeter is connected in series with the required device, Voltmeter in Parallel
(b)Both Ammeter and Voltmeter are connected in series with required device
The Voltmeter is connected in series with the device, Ammeter in parallel
(d)They can be connected in any way.

रासायनिक यौगिक और उनके सामान्य नाम

    

1. आम नाम: बेकिंग पाउडर

 रासायनिक यौगिक: सोडियम बाइकार्बोनेट

 रासायनिक सूत्र: NaHCO3

 2. आम नाम: ब्लू विट्रिओल

 रासायनिक यौगिक: कॉपर सल्फेट

 रासायनिक सूत्र: CuSO4।  XH2O

 3. आम नाम: ब्लीचिंग पाउडर

 रासायनिक यौगिक: कैल्शियम ऑक्सीक्लोराइड

 रासायनिक सूत्र: CaOCL2

 4. आम नाम: क्लोरोफॉर्म

 रासायनिक यौगिक: ट्राइक्लोरो मिथेन

 रासायनिक सूत्र: CHCl3

 5. आम नाम: चाक (संगमरमर)

 रासायनिक यौगिक: कैल्शियम कार्बोनेट

 रासायनिक सूत्र: CaCo3

 6. आम नाम: कास्टिक पोटाश

 रासायनिक यौगिक: पोटेशियम हाइड्रॉक्साइड

 रासायनिक सूत्र: KOH

 7. आम नाम: कास्टिक सोडा

 रासायनिक यौगिक: सोडियम हाइड्रॉक्साइड

 रासायनिक सूत्र: NaOH

 8. आम नाम: सूखी बर्फ

 रासायनिक यौगिक: ठोस कार्बोंडाईऑक्साइड

 रासायनिक सूत्र: CO2

 9. आम नाम: एप्सोम

 रासायनिक यौगिक: मैग्नीशियम सल्फेट

 रासायनिक सूत्र: MgSo4

 10. आम नाम: जिप्सम

 रासायनिक यौगिक: कैल्शियम सल्फेट

 रासायनिक सूत्र: CaSo4।  2H2O

 11. आम नाम: ग्रीन विट्रियल

 रासायनिक यौगिक: लौह सल्फेट

 रासायनिक सूत्र: FeSo4

 12. आम नाम: भारी पानी

 रासायनिक यौगिक: ड्यूटेरियम ऑक्साइड

 रासायनिक सूत्र: D2O

 13. आम नाम: सिरका

 रासायनिक यौगिक: एसिटिक एसिड

 रासायनिक सूत्र: CH3COOH

 14. आम नाम: वॉशिंग सोडा

 रासायनिक यौगिक: सोडियम कार्बोनेट

 रासायनिक सूत्र: Na2CO3

 15. कॉमन नेम्स: स्लेक्ड लाइम

 रासायनिक यौगिक: कैल्शियम हाइड्रॉक्साइड

 रासायनिक सूत्र: सीए (ओएच) 2

 16. आम नाम: पोटाश एलम

 रासायनिक यौगिक: पोटेशियम एल्यूमीनियम सल्फेट

 रासायनिक सूत्र: KAl (SO₄) ₂ · 12H .O

 17. आम नाम: त्वरित चूना

 रासायनिक यौगिक: कैल्शियम ऑक्साइड

 रासायनिक सूत्र: CaO

 18. आम नाम: प्लास्टर ऑफ पेरिस

 रासायनिक यौगिक: कैल्शियम सल्फेट

 रासायनिक सूत्र: CaSO4।  1/2 एच 2 ओ

 19. आम नाम: मोहर का नमक

 रासायनिक यौगिक: अमोनियम फेरस सल्फेट

 रासायनिक सूत्र: (NH4) 2Fe (SO4) 2 · 6H2O

 20. आम नाम: सफेद विट्रियल

 रासायनिक यौगिक: जिंक सल्फेट

 रासायनिक सूत्र: ZnSo4.7H2O

 21. आम नाम: मार्श गैस

 रासायनिक यौगिक: मिथेन

 रासायनिक सूत्र: सीएच 4

 22. आम नाम: मैग्नेशिया

 रासायनिक यौगिक: मैग्नीशियम ऑक्साइड

 रासायनिक सूत्र: MgO

 23. आम नाम: लाफिंग गैस

 रासायनिक यौगिक: नाइट्रस ऑक्साइड

 रासायनिक सूत्र: N2O

 24. आम नाम: सिंदूर

 रासायनिक यौगिक: मरक्यूरिक सल्फाइड

 रासायनिक सूत्र: HgS

 25. आम नाम: चीनी

 रासायनिक यौगिक: सुक्रोज

 रासायनिक सूत्र: C12H22O11

 26. सामान्य नाम: T.N.T.

 रासायनिक यौगिक: ट्रिनिट्रोटोलुइन

 रासायनिक सूत्र: C7H5N3O6

 27. आम नाम: रेत

 रासायनिक यौगिक: सिलिकॉन ऑक्साइड

 रासायनिक सूत्र: SiO2

CHEMICAL FORMULAS AND THEIR COMMON NAMES

       

1. Common Names: Baking Powder

Chemical Compounds: Sodium Bicarbonate

Chemical Formula: NaHCO₃

2. Common Names: Blue Vitriol

Chemical Compounds: Copper Sulphate

Chemical Formula: CuSO₄. XH₂O

3. Common Names: Bleaching Powder

Chemical Compounds: Calcium Oxychloride

Chemical Formula: CaOCL₂

4. Common Names: Chloroform

Chemical Compounds: Trichloro Methane

Chemical Formula: CHCl₃

5. Common Names: Chalk (Marble)

Chemical Compounds: Calcium Carbonate

Chemical Formula: CaCo₃

6. Common Names: Caustic Potash

Chemical Compounds: Potassium Hydroxide

Chemical Formula: KOH

7. Common Names: Caustic Soda

Chemical Compounds: Sodium Hydroxide

Chemical Formula: NaOH

8. Common Names: Dry Ice

Chemical Compounds: Solid Carbondioxide

Chemical Formula: CO₂

9. Common Names: Epsom

Chemical Compounds: Magnesium Sulphate

Chemical Formula: MgSo₄

10. Common Names: Gypsum

Chemical Compounds: Calcium Sulphate

Chemical Formula: CaSo₄. 2H₂O

11. Common Names: Green Vitriol

Chemical Compounds: Ferrous Sulphate

Chemical Formula: FeSo₄

12. Common Names: Heavy Water

Chemical Compounds: Deuterium Oxide

Chemical Formula: D₂O

13. Common Names: Vinegar

Chemical Compounds: Acetic Acid

Chemical Formula: CH₃COOH

14. Common Names: Washing Soda

Chemical Compounds: Sodium Carbonate

Chemical Formula: Na₂CO₃

15. Common Names: Slaked Lime

Chemical Compounds: Calcium Hydroxide

Chemical Formula: Ca(OH)₂

16. Common Names: Potash Alum

Chemical Compounds: Potassium Aluminium Sulphate

Chemical Formula: KAl(SO₄)₂·12H₂O

17. Common Names: Quick Lime

Chemical Compounds: Calcium Oxide

Chemical Formula: CaO

18. Common Names: Plaster of Paris

Chemical Compounds: Calcium Sulphate

Chemical Formula: CaSO₄. 1/2 H₂O

19. Common Names: Mohr's Salt

Chemical Compounds: Ammonium Ferrous Sulphate

Chemical Formula: (NH₄)₂Fe(SO₄)₂·6H₂O

20. Common Names: White Vitriol

Chemical Compounds: Zinc Sulphate

Chemical Formula: ZnSo₄.7H₂O

21. Common Names: Marsh Gas

Chemical Compounds: Methane

Chemical Formula: CH₄

22. Common Names: Magnesia

Chemical Compounds: Magnesium Oxide

Chemical Formula: MgO

23. Common Names: Laughing Gas

Chemical Compounds: Nitrous Oxide

Chemical Formula: N₂O

24. Common Names: Vermelium

Chemical Compounds: Mercuric Sulphide

Chemical Formula: HgS

25. Common Names: Sugar

Chemical Compounds: Sucrose

Chemical Formula: C₁₂H₂₂O₁₁

26. Common Names: T.N.T.

Chemical Compounds: Trinitrotoluene

Chemical Formula: C₇H₅N₃O₆

27. Common Names: Sand

Chemical Compounds: Silicon Oxide

Chemical Formula: SiO₂

Monotremes

Egg-laying Mammals

Echidna. Photo by Dr. Lloyd Glenn Ingles © 2001 California Academy of Sciences.   There are only five living monotreme species: the duck-billed platypus and four species of echidna (also known as spiny anteaters). All of them are found only in Australia and New Guinea. Monotremes are not a very diverse group today, and there has not been much fossil information known until rather recently. In some ways, monotremes are very primitive for mammals because, like reptiles and birds, they lay eggs rather than having live birth. In a number of other respects, monotremes are rather derived, having highly modified snouts or beaks, and modern adult monotremes have no teeth. Like other mammals, however, monotremes have a single bone in their lower jaw, three middle ear bones, high metabolic rates, hair, and they produce milk to nourish the young. Monotremes are one of the three main groups of living mammals, along with placentals and marsupials. The monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts compared to the more common mammalian types.  Order: Monotremata Scientific name: Monotremata Class: Mammalia Phylum: Chordata Kingdom: Animalia MONOTREME Gestation period Platypus: 10 – 14 days Short-beaked echidna: 18 days Western long-beaked echidna: 10 days