JAMB Past Questions and Answers - Page 1535

7,671.

Elements X and Y have electronic configurations 1s\(^2\)2s\(^2\)2p\(^4\) and 1s\(^2\)2s\(^2\)2p\(^2\)3s\(^6\)3p\(^1\) respectively. When they combine, the formula of the compound formed is?

A.

XY

B.

YX

C.

X2Y3

D.

Y2X3

Correct answer is D

\(\frac{\text{Element X}}{1s^22s^21p^4}\)

Valency of X is 2


\(\frac{\text{Element Y}}{1s^22s^22p^63s^23P^1}\)

valency of Y is 3

There is an exchange of valency when a compound is being formed. Hence, we have Y\(_2\)X\(_3\)

7,672.

The atomic radius of Li, Na and K are 1: 33A, 1. 54A and 1. 96A res pectively. Which of the following explaqins this gradation in atomic radius?

A.

electropositivity decreases from Li to Na to K

B.

electronegativity decreases from Li to Na to K

C.

the number of the electron shells increases from Li to Na to K

D.

the elements are in the same period

Correct answer is C

No explanation has been provided for this answer.

7,674.

The minimum volume of oxygen required for the complete combustion of a mixture of 10cm 3 of CO and 15 cm 3 of H 2 is

A.

25.0cm3

B.

12.5 cm3

C.

10.0 cm3

D.

5.0cm3

Correct answer is B

No explanation has been provided for this answer.