Question

4.	Which two electron configurations represent elements that would have similar chemical properties? (1) 1s22s22p4       (2) 1s22s22p5       (3) [Ar]4s23d5       (4) [Ar]4s23d104p5
	A)	(1) and (2)
	B)	(1) and (3)
	C)	(2) and (3)
	D)	(2) and (4)
	E)	(3) and (4)
5.	Which of the following make an isoelectronic pair: Cl–, O2–, F, Ca2+, Fe3+?
	A)	Ca2+ and Fe3+
	B)	O2– and F
	C)	F and Cl–
	D)	Cl– and Ca2+
	E)	None of the above.

6.	Which of the following is the electron configuration of the iron(III) ion?
	A)	[Ar]3d5
	B)	[Ar]4s13d5
	C)	[Ar]4s23d3
	D)	[Ar]3d6
	E)	[Ar]4s23d9

7.	Which of the following ion has unpaired electrons in its orbitals?
	A)	P3–
	B)	V5+
	C)	Mg2+
	D)	Sc2+
	E)	S2-

Answer 1

4. (1) 1s2 , 2s2 2p4

(2) 1s2 , 2s2 2p5

(3) [Ar]4s2 , 3d5

(4) [Ar]4s2 , 3d10 , 4p5

It can be seen that, electronic configurations (2) & (4) follow the same trend. The outer electronic configuration is same in both cases. Hence the elements belongs to the same group.

Thus, elements with electron configurations (2) & (4) have similar chemical properties.

5. Number of electrons in the given species are -

Cl- = 18

O2- = 10

F = 9

Ca2+ = 18

Fe3+ = 23

Among the given species, Cl- and Ca2+ have the same number of electrons.

Hence, Cl- and Ca2+ are the isoelectronic species.

6. iron(III) ion

Fe3+ = 23

Electronic configuratiob of Fe3+ ion is given as -

Fe3+ : 1s2 , 2s2 2p6 , 3s2 3p6 3d5

Fe3+ = [Ar] 3d5

7. The electronic configaration of the ions is given as -

(A) P3- : [Ar] = 1s2 2s2 2p6 3s2 3p6

(B) V5+ : [Ar] = 1s2 2s2 2p6 3s2 3p6

(C) Mg2+ : [Ne] = 1s2 2s2 2p6

(D) Sc2+ : [Ar] 3d1

(E) S2- : [Ar] = 1s2 2s2 2p6 3s2 3p6

Hence, Sc2+ have unpaired electron.