Question

Among the statements (I–IV), the correct ones are:

(I) $\mathrm{Be}$ has a smaller atomic radius compared to $\mathrm{Mg}$.

(II) $\mathrm{Be}$ has higher ionization enthalpy than $\mathrm{Al}$.

(III) Charge/radius ratio of $\mathrm{Be}$ is greater than that of $\mathrm{Al}$.

(IV) Both $\mathrm{Be}$ and $\mathrm{Al}$ form mainly covalent compounds.

• A. (I), (II) and (IV)
• B. (I), (II) and (III)
• C. (II), (III) and (IV)
• D. (I), (III) and (IV)

Answer 1

The correct option is A

(I), (II) and (IV)

Explanation for correct option:

(A) (I), (II) and (IV)

Statement (I):

1. $\mathrm{Be}$ has a smaller atomic radius compared to $\mathrm{Mg}$.
2. This is so because down the group size of elements increases and in periodic table $\mathrm{Be}$ and $\mathrm{Mg}$ are elements of same group but $\mathrm{Be}$ is placed above $\mathrm{Mg}$, so it is smaller in size.

Statement (II):

1. $\mathrm{Be}$ has higher ionization enthalpy than $\mathrm{Al}$.
2. This is so because $\mathrm{Be}$ has full filled s-subshell electronic configuration $\left(1{\mathrm{s}}^2,2{\mathrm{s}}^2\right)$so it require more energy to remove electron from full filled subshell.

Statement (IV):

1. Both $\mathrm{Be}$ and $\mathrm{Al}$ form mainly covalent compounds.
2. This is so because these elements have high second ionization enthalpies.
3. So they form covalent bonds by sharing electrons rather than forming ionic bonds by donating electrons.

Explanation for incorrect options:

(B) (I), (II) and (III)

1. From the above discussion it can be observed that statement (I) and (II) are correct.
2. Statement (III): Charge/radius ratio of $\mathrm{Be}$ is greater than that of $\mathrm{Al}$.
3. This is so because $\mathrm{Be}$ and $\mathrm{Al}$ have similar charge/radius ratio as they exhibit diagonal relationship.
4. Hence, the statement is incorrect.

(C) (II), (III) and (IV)

From the above discussion, it can be observed that statement (II) and (IV) are correct but statement (III) is incorrect.

(D) (I), (III) and (IV)

From the above discussion, it can be observed that statement (I) and (IV) are correct but statement (III) is incorrect.

Hence option C is correct, statements (I), (II) and (IV) are correct.