Question

Assertion: Lattice energy of $CaO$ is higher than that of $NaCl$.

Reason: The lattice energy of an ionic compund is directly proportional to the product of the charges of ions.

• A. Both the assertion and the reason are true and the reason is the correct explanation of the assertion
• B. Both the assertion and the reason are true but the reason is not the correct explanation of the assertion
• C. The assertion is true but the reason is false
• D. Both the assertion and the reason are false

Answer 1

The correct option is A Both the assertion and the reason are true and the reason is the correct explanation of the assertion

Lattice energy is directly proportional to the product of charges of ions and inversely proportional to the size of ions (interionic distance between ions).
Here, calcium ion $\left(C{a}^{2+}\right)$ is not only smaller than sodium ion $\left(N{a}^{+}\right)$ but also has twice the charge as that of the sodium ion. Similarly, the oxide ion$\left(O^{2-}\right)$ also has a much smaller size and higher charge (magnitude wise) as compared to the chloride ion $\left(C{l}^{-}\right)$. Hence, due to these reasons, the lattice energy of $CaO$ is higher than that of $NaCl$.