WAEC Chemistry Past Questions & Answers - Page 91

451.

\(Cu_2S_{(s)}+ O_{2(g)} = 2CU_{(s)} + SO_{2(g)}\).

In the above reaction, the oxidation number of Cu changes from ___ to _______?

A.

+1 to 0

B.

0 to +2

C.

+2 to +1

D.

0 to +1

Correct answer is A

The oxidation number is from +1 to O as a result of the release of sulphur. Options B, C, and D are not the actual oxidation number for copper

452.

All these are electromagnetic waves except

A.

White light

B.

Photon

C.

X-ray

D.

Infrared

Correct answer is B

Photon is unit of energy that carries light and has zero mass A, C and D are all electromagnetic waves of higher mass

453.

Which of these radioactive elements is commonly used as a nuclear fuel

A.

uranium

B.

palladium

C.

actium

D.

thorium

Correct answer is A

Uranium is common nuclear because of its less stability as a result has a great tendency to increase energy than. Options B,C,D which are not stable

454.

A major source of oxide of nitrogen is from the burning of

A.

coal

B.

wood

C.

fuel

D.

chlorofluorocarbons

Correct answer is C

No explanation has been provided for this answer.

455.

Rare gases are stable because they

A.

are monoatomic

B.

form ions easily

C.

have duplet or octet electronic configuration in the outermost shells in their atoms

D.

are volatile gases

Correct answer is C

Rare gases are stable because they have duplet or octet electronic configurations in the outermost shells in their atoms, as a result they don’t go into solution easily. option A, B, Dare not because they go into solution easily (unstable)