Final answer:
The greater lattice energy of CrCl2 compared to MnCl2 is due to the smaller ionic radius of chromium, leading to shorter interionic distances and therefore stronger electrostatic attractions within the lattice.
Step-by-step explanation:
The question focuses on understanding why CrCl2 has greater lattice energy compared to MnCl2, given the choices provided. Lattice energy is influenced by the ionic charges and the interionic distances of the participating cations and anions in the crystal lattice. Among the options given, the correct reason is related to the size of the cation, which affects the interionic distance and thus the lattice energy. Specifically, the ionic radius of chromium (Cr2+) is smaller than that of manganese (Mn2+), leading to a shorter interionic distance which corresponds to a greater lattice energy for CrCl2. This is because a smaller cation can approach the anions more closely in the crystal lattice, resulting in stronger electrostatic attractions within the lattice structure. Hence, option B is the most accurate explanation for the greater lattice energy of CrCl2 compared to MnCl2.