Which of the following statements are true? Choose the correct answer from the options given below :
- C and D only
- A, C, and E only
- A, B, and E only
- C and E only
Answer
(4) C and E only
Solution
A. False: Ga does not have a high melting point. As per NCERT, Ga melts at 303 K and Cs at 302 K; both have very low melting points.
B. False: on the Pauling scale, N = 3.0 and Cl = 3.0, i.e. the values are the same.
C. True: each species has 18 electrons: Ar (18), K+ (19 − 1), Cl- (17 + 1), Ca2+ (20 − 2), S2- (16 + 2).
D. False: i H1 ( kJ mol-1): Na 496, Mg 737, Al 577, Si 786.
∵ The 3p electron of Al is shielded by the filled 3s orbital and is removed more easily than a 3s electron of Mg.
∴ Correct order: Si > Mg > Al > Na
E. True: atomic (metallic) radius increases down a group: Li (152 pm) < Rb (248 pm) < Cs (265 pm).
∴ Correct statements: C and E only.
Answer: (4)