Question

Assertion (A) : Actinoids show wide range of oxidation states.
Reason (R) : This is due to comparable energies of 5f, 6d and 7s orbitals.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Actinoids have 5f, 6d and 7s orbitals of comparable energy, so many electrons can take part in bonding. R explains A.

Answer 1

The Correct Option is A

Step 1: Read the two statements:
A says actinoids have a wide range of oxidation states. R gives the reason as comparable energies of $5f$, $6d$ and $7s$ orbitals.

Step 2: Test A with examples:
The early actinoids Th to Am show oxidation states from +3 up to +7. Neptunium, for instance, shows +3, +4, +5, +6 and +7. A wide range is therefore true.

Step 3: Test R against the electron configuration:
The energy gap between $5f$, $6d$ and $7s$ is small. This is a standard NCERT fact, so R is true.

Step 4: Link R to A:
Electrons of the $5f$ subshell are not held tightly because the orbitals are so close to $6d$ and $7s$. Different numbers of them can therefore join in bonding. This is the cause of the variable oxidation states, so R explains A.
Option (B) is wrong because R is the explanation. Options (C) and (D) are wrong because neither statement is false.

Final Answer:
Option (A) is correct. \[ \boxed{\text{(A)}} \]