1099+ Important Chemistry MCQ Questions Answers

Q:

Which of the following substances cause temporary hardness in water?

1. Mg(HCO3)2

2. Ca(HCO3)2

3. CaCl2

4. MgSO4

A) 3 and 4	B) 2and 3
C) 1 and 4	D) 1 and 2

Answer & Explanation Answer: D) 1 and 2

Explanation:

There are two types of water hardness: temporary and permanent hardness. Temporary hardness is due to the presence of calcium hydrogen carbonate Ca(HCO3)2(aq) and magnesium hydrogen carbonate Mg(HCO3)2(aq).

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0 18078

Q:

Consider the following constituent gases of the atmosphere :

1. Argon

2. Neon

3. Helium

4.Ceirbon dioxide

Which one of the following is the correct ascending sequence of the above gases in terms of the volume percentage?

A) 1-3-2-4	B) 1-4-2-3
C) 4-2-3-1	D) 2-4-1-3

Answer & Explanation Answer: B) 1-4-2-3

Explanation:

Composition of Dry Air (Substance, % by volume)

Nitrogen, N2 78.08

Oxygen, O2

20.95

Argon, Ar 0.93

Carbon dioxide, CO2 0.033

Neon, Ne 0.0018

Helium, He 0.00052

Methane, CH4 0.0002

Krypton, Kr 0.00011

Dinitrogen oxide, N2O 0.00005

Hydrogen, H2 0.00005

Ozone, O3 0.000001

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Q:

Which solution is most concentrated?

A) 6 g of solute in 10 ml of solution	B) 20.5 g of solute in 50 ml of solution
C) 30 g of solute in 120 ml of solution	D) 2.6 g of solute in 2 ml of solution

Answer & Explanation Answer: D) 2.6 g of solute in 2 ml of solution

Explanation:

A concentrated solution will contain the most solute molecules per solvent molecules.

Here in the given options,

1) 6/10 = 0.6

2) 20.5/50 = 0.41

3) 30/120 = 0.25

4) 2.6/2 = 1.3

Hence, option D) is most concentrated.

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21 17729

Q:

Which of the following statement(s) is/are INCORRECT?

I. Alkenes are fairly unreactive.

II. Alkenes burn with blue flame.

III. Alkanes burn with yellow flame.

A) Only I and II	B) Only I and III
C) Only II and III	D) All I, II and III

Answer & Explanation Answer: D) All I, II and III

Explanation:

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Q:

Which of the following statements are CORRECT?

I. Ethanol is a good solvent for organic compounds.

II. Boiling and melting points of ethanol are low with respect to water.

III. Ethanol is used tincture iodine

A) Only I and II	B) Only I and III
C) Only II and III	D) All I, II and III

Answer & Explanation Answer: D) All I, II and III

Explanation:

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Q:

NH3 oxidation number?

A) -1	B) +1
C) 0	D) -3

Answer & Explanation Answer: C) 0

Explanation:

NH3, Ammonia is a neutral compound as the individual oxidation numbers elements that make up the compound NH3 are Nitrogen (N) and Hydrogen (H) sum to zero.

We do not speak of the oxidation number of a molecule. We can speak of the oxidation numbers of the individual elements that make up the compound.

Here the oxidation number of Nirogen is -3 and that of Hydrogen is +1.

Now, NH3 = 1(-3) + 3(+1) = -3 + 3 = 0.

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30 17268

Q:

The absolute value of charge on electron was determined by

A) J.J.Thomson	B) R.A. Millikan
C) Rutherford	D) Chadwick

Answer & Explanation Answer: B) R.A. Millikan

Explanation:

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59 17194

Q:

Valency of an element depends on which of the following?

I. Number of losing electron

II. Number of gaining electron

III. Number of sharing electron

A) Only I and II	B) Only I and III
C) Only II and III	D) All I, II and III

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