The melting point of RbBr is 682°C, while that of NaF is 988°C. The principal reason that the melting point of NaF is much higher than that of RbBr is that:

JEE Main Chemistry question

The melting point of RbBr is , while that of NaF is . The principal reason that the melting point of NaF is much higher than that of RbBr is that:

(A)The two crystals are not isomorphous
(B)The molar mass of NaF is smaller than that of RbBr
(C)The internuclear distance is greater for RbBr than for NaFCorrect
(D)The bond in RbBr has more covalent character than the bond in NaF

Answer: (C)

Solution

and are both considerably larger ions than and , so the interionic distance — and hence the separation between oppositely charged ions in the lattice — is greater in RbBr than in NaF. Since lattice (and hence melting-point-related cohesive) energy varies inversely with this

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Question ID VK-141645