1099+ Important Chemistry MCQ Questions Answers

Q:

The most abundant metal in earth crust is

A) Iron	B) magnesium
C) calcium	D) aluminium

Answer & Explanation Answer: D) aluminium

Explanation:

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6 4687

Q:

Which one of the following orders presents the correct sequence of the increasing basic nature of the given oxides?

(1) $K_{2} O < N a_{2} O < A l_{2} O_{3} < M g O$

(2) $A l_{2} O_{3} < M g O < N a_{2} O < K_{2} O$

(3) $M g O < K_{2} O < A l_{2} O_{3} < N a_{2} O$

(4) $N a_{2} O < K_{2} O < M g O < A l_{2} O_{3}$

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

Answer & Explanation Answer: B) Option 2

Explanation:

While moving from left to right in periodic table basic character of oxide of elements will decrease.

$∴ \to_{I n c r e a \sin g b a s i c s t r e n g t h}^{A l_{2} O_{3} < M g O < N a_{2} O}$

and while descending in the group basic character of corresponding oxides increases.

$∴ \to_{I n c r e a \sin g b a s i c s t r e n g t h}^{N a_{2} O < K_{2} O}$

$∴ C o r r e c t O r d e r i s A l_{2} O_{3} < M g O < N a_{2} O < K_{2} O$

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Q:

Chloroform used as anaesthetic should be preserved in the dark in tightly stoppered bottles because otherwise

A) it becomes coloured	B) it gets evaporated in air
C) it gets oxidised to phosgene	D) it gets decomposed to chloropicrin

Answer & Explanation Answer: C) it gets oxidised to phosgene

Explanation:

Chloroform, $C H C l_{3}$ is easily oxidised to the highly poisonous gas known as phosgene or carbonyl chloride COCl2. Hence if it is used as anaesthetic it should be kept free from sunlight and air.

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9 4594

Q:

Which reaction occurs spontaneously?

A) Cl2(g) + 2NaF(aq)--> F2(g) + 2NaCl(aq)	B) I2(s) + 2NaF(aq)--> F2(g) + 2NaI(aq)
C) Cl2(g) + 2NaBr(aq)-->Br2(l) + 2NaCl(aq)	D) I2(s) + 2NaBr(aq)--> Br2(l) + 2NaI(aq)

Answer & Explanation Answer: C) Cl2(g) + 2NaBr(aq)-->Br2(l) + 2NaCl(aq)

Explanation:

In this chemical reaction chlorine change oxidation number from 0 to -1 (reduction) and bromine change oxidation number from -1 to 0 (oxidation).

Chlorine is stronger oxidation reagent than bromine.

In VIIA or group 17 (halogen elements) there are six elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At) and tennessin(Ts).

They have high electronegativity because they have seven valence electrons in their outermost energy level, so they can gain an electron to have the octet rule.

Going down in the group, element are weaker oxidazing reagent and less reactive.

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2 4592

Q:

Which one of the following can be oxidised to the corresponding carbonyl compound:

A) 2-methyl-2-hydroxy propane	B) 2-hydroxy propane
C) o-Nitrophenol	D) Phenol

Answer & Explanation Answer: B) 2-hydroxy propane

Explanation:

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12 4569

Q:

Which one of the following laws directly expalins the law of coservation of mass

A) Hund's rule	B) Dalton's law
C) Avogadro's law	D) Berzelius hypothesis

Answer & Explanation Answer: C) Avogadro's law

Explanation:

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8 4522

Q:

Of the following radiations, the most easily stopped by air

A) alpha - rays	B) beta - rays
C) gamma -rays	D) x - rays

Answer & Explanation Answer: A) alpha - rays

Explanation:

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2 4462

Q:

Which one of the following laws explain the formation of carbon monoxide and carbon dioxide from carbon and oxygen

A) Laws of conservation of mass	B) Laws of multiple proportion
C) Laws of reciprocal proportions	D) Law of definite proportions

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