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Chemistry questions and answers

Chemistry Questions and Answers

Learn more about the properties, composition, and structure of substances (elements and compounds) with these Chemistry questions and answers. This Test can be used by students preparing for Chemistry in JAMB, WAEC, NECO or Post UTME.

21.

The periodic property that is used to determine whether a covalent molecule is polar or not is

A.

atomic radius

B.

ionization energy

C.

electron affinity

D.

electronegativity

Correct answer is D

The periodic property that is used to determine whether a covalent molecule is polar or not is electronegativity.

Electronegativity is a measure of the ability of an atom to attract electrons in a chemical bond. The greater the electronegativity of an atom, the more strongly it will attract electrons.

22.

The gas that is less dense than air is

A.

nitrogen

B.

chlorine

C.

Carbon(IV) oxide

D.

Oxygen

Correct answer is A

The density of a gas is directly proportional to its molar mass. This means that gases with a lower molar mass will be less dense than gases with a higher molar mass. Nitrogen (N2) has a molar mass of 28 g/mol, which is less than that of air (approximately 29 g/mol), making it less dense than air.

23.

The primary component of natural gas

A.

ethane

B.

methane

C.

butane

D.

propane

Correct answer is B

Natural gas is a fossil fuel primarily composed of hydrocarbon gases. The primary component of natural gas is methane, which typically makes up a significant portion of the gas mixture. Methane is a simple hydrocarbon with one carbon atom and four hydrogen atoms (CH4). It is the main component of natural gas, often accounting for over 90% of its composition.

24.

Going down group II in the periodic table normally

A.

ionization energy increases

B.

melting point increases

C.

shielding effect decreases

D.

electronegativity increases

Correct answer is B

Melting point increases. This is because the atoms become larger as you go down the group, which means that the metallic bonds between them become stronger.

25.

How many unpaired electrons are present in 26Fe3+?

A.

4

B.

2

C.

3

D.

5

Correct answer is D

There are 5 unpaired electrons present in 26Fe3+.

The atomic number of iron is 26, so it has 26 electrons. When iron loses 3 electrons to form Fe3+, it loses 2 from the s orbital and 1 from the d orbital. This leaves 5 unpaired electrons in the d orbital.

The electron configuration of Fe3+ is [Ar]3d5. The 5 d electrons are all unpaired because Hund's rule states that electrons will occupy degenerate orbitals singly before they pair up. This is because unpaired electrons have a lower energy than paired electrons.