Use Fajans’ rule to compare covalent character

Covalent character in an ionic compound increases when:

• the cation is small and highly polarising,
• the anion is large and highly polarizable.

So:

• smaller cation $\Rightarrow$ more covalent character,
• larger anion $\Rightarrow$ more covalent character.

Check each statement

Statement A: $\mathrm{KF > KI;\ LiF > KF}$

• Compare $\mathrm{KF}$ and $\mathrm{KI}$:

  • same cation $\mathrm{K^+}$,
  • $\mathrm{I^-}$ is larger than $\mathrm{F^-}$,
  • hence $\mathrm{KI}$ has more covalent character than $\mathrm{KF}$.

  Therefore, $\mathrm{KF > KI}$ is false; correct order is $\mathrm{KF < KI}$

• Compare $\mathrm{LiF}$ and $\mathrm{KF}$:

  • same anion $\mathrm{F^-}$,
  • $\mathrm{Li^+}$ is smaller than $\mathrm{K^+}$,
  • so $\mathrm{Li^+}$ polarises more strongly.

  Hence, $\mathrm{LiF > KF}$ is true.

Since first part is false, Statement A is false.

Statement B: $\mathrm{KF < KI;\ LiF > KF}$

From above:

• $\mathrm{KF < KI}$ is true,
• $\mathrm{LiF > KF}$ is true.

Hence Statement B is true.

Statement C: $\mathrm{SnCl_4 > SnCl_2;\ CuCl > NaCl}$

• Compare $\mathrm{SnCl_4}$ and $\mathrm{SnCl_2}$:

  • cation in $\mathrm{SnCl_4}$ is effectively $\mathrm{Sn^{4+}}$,
  • cation in $\mathrm{SnCl_2}$ is effectively $\mathrm{Sn^{2+}}$,
  • higher charge means greater polarising power.

  Therefore, $\mathrm{SnCl_4 > SnCl_2}$ is true.

• Compare $\mathrm{CuCl}$ and $\mathrm{NaCl}$:

  • $\mathrm{Cu^+}$ has greater polarising power than $\mathrm{Na^+}$ due to smaller size and pseudo-inert gas configuration effect,
  • therefore $\mathrm{CuCl}$ is more covalent than $\mathrm{NaCl}$.

  So, $\mathrm{CuCl > NaCl}$ is true.

Hence Statement C is true.

Statement D: $\mathrm{LiF > KF;\ CuCl < NaCl}$

• $\mathrm{LiF > KF}$ is true,
• but $\mathrm{CuCl < NaCl}$ is false because actually $\mathrm{CuCl > NaCl}$

Hence Statement D is false.

Statement E: $\mathrm{KF < KI;\ CuCl > NaCl}$

• $\mathrm{KF < KI}$ is true,
• $\mathrm{CuCl > NaCl}$ is true.

Hence Statement E is true.

Collect the correct statements

Correct statements are: $\boxed{\text{B, C, and E}}$

Match with given options

The option containing $\mathrm{B, C, E\ only}$ is: $\boxed{\text{D}}$

Comparison with stored correct answer

Stored correct answer = $\boxed{\text{D}}$

My derived answer also = $\boxed{\text{D}}$.

So they agree.