1099+ Important Chemistry MCQ Questions Answers

Q:

$Mg + O_{2} = MgO$

Balance the above Chemical equation?

A) 2Mg + O2 ----> 2MgO	B) 2Mg + O ----> 2MgO
C) 2Mg + O ----> MgO2	D) 2Mg + O2 ----> MgO2

Answer & Explanation Answer: A) 2Mg + O2 ----> 2MgO

Explanation:

Given Equation is

$Mg + O_{2} \to MgO$

Balancing the Chemical Equation is nothing but Conservation of Matter. As Matter is Neither created nor Destroyed, it must be conserved.

Here we have 1 Mg and 2 O on the left side and 1 Mg and 1 O on the right side

To balance that, add 1 Mg on the left side so that it becomes 2 Mg and 2 O on the left side

i.e,

$2 Mg + O_{2} \to 2 MgO$

Here it has 2 Mg & 2 O on the left side and 2 Mg and 2 O on the right side and the Chemical equation is Balanced.

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Q:

What is the Iupac name for the compound shown below.

clbr1527920257.png image

A) 1-Bromo-3-chlorocyclohexene	B) 2-Bromo-6-chlorocyclohex-1-ene
C) 6-Bromo-2-chlorocyclohexene	D) 3-Bromo-1-chlorocyclohex-1-ene

Answer & Explanation Answer: D) 3-Bromo-1-chlorocyclohex-1-ene

Explanation:

In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC).

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Q:

which of the following are chemical changes?

A) Cooking of Food

B) Digestion of Food

C) Freezing of water

D) Water is heated up

A) A & B	B) A, B & C
C) C & D	D) All the above

Answer & Explanation Answer: A) A & B

Explanation:

A) Cooking of Food ------ Chemical Change

B) Digestion of Food ----- Chemical Change

C) Freezing of water ----- Physical Change

D) Water is heated up ---- Physical Change

because here the chemical composition of the substance changes in A & B only.

Since we know that, If the chemical composition is changing then it is a chemical change and if the chemical composition is remaining the same, then it is a physical change.

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Q:

Silver Mirror test is given by which one of the following compounds?

1. Benzophenone

2. Acetaldehyde

3. Acetone

4. Formaldehyde

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

Answer & Explanation Answer: D) 2 and 4

Explanation:

Both Formaldehyde and Acetaldehyde will give this test

$H C H O \overset{[A g (N H_{3})_{2}^{+}]}{\to} \overset{A g}{S i l v e r m i r r o r} + O r g a n i c c o m p o u n d$

$C H_{3} - C H O \overset{[A g (N H_{3})_{2}^{+}]}{\to} \underset{S i l v e r m i r r o r}{A g} + O r g a n i c c o m p o u n d$

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Q:

what is the chemical name of the compound

${Cu}_{2} {CO}_{3}$

A) copper (ii) carbonate	B) copper (iii) carbonate
C) copper (i) carbonate	D) copper carbonate

Answer & Explanation Answer: C) copper (i) carbonate

Explanation:

The chemical name of the compound

${Cu}_{2} {CO}_{3 is}$ Copper (i) carbonate and is also called as cuprous carbonate.

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Q:

Place these hydrocarbons in order of decreasing boiling point.

1. Paraffin

2. Octadecane

3. Hexane

4. Neohexane and

5. Ethane

A) Paraffin > Octadecane > Neohexane > Hexane > Ethane	B) Paraffin > Octadecane > Hexane > Neohexane > Ethane
C) Hexane > Paraffin > Octadecane > Neohexane > Ethane	D) None of the above

Answer & Explanation Answer: B) Paraffin > Octadecane > Hexane > Neohexane > Ethane

Explanation:

In hydrocarbon, the boiling point directly varies with the length of carbon chain. On increasing the number of carbon atom, the boiling point of the compound also increases. Paraffin contains highest number of carbon atoms whereas, ethane is comprised of two carbon atoms.

The decreasing order of boiling point of mention compounds is written as follows:

Paraffin > Octadecane > Hexane > Neohexane > Ethane

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Q:

Which are two chemicals used to purify water?

A) Chlorine & Fluorine	B) Fluorine & Iodine
C) Chlorine & Hydrogen peroxide	D) Fluorine & Iodine

Answer & Explanation Answer: C) Chlorine & Hydrogen peroxide

Explanation:

Removing the contaminents if any in the water which causes harm to our health is involved in the purifying of water.

This process involves chemicals. Chloramines, Hydrogen peroxide, Iodine are the chemicals which are used in purifying water.

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Q:

Which of the following group is NOT Dobereiner Triads?

A) Li, Na, K	B) N, P Au
C) Cl, Br, I	D) Ca, Sr, Ba

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