Question

Match the following \[ \begin{array}{|c|c|} \hline \text{List-I} & \text{List-II} \\ \hline \text{A. Co, Ni} & \text{I. Electronegativity} \\ \text{B. K, Ba} & \text{II. Electron gain enthalpy} \\ \text{C. N, Cl} & \text{III. Metallic radius} \\ \text{D. Ar, Kr} & \text{IV. Standard reduction potential (-ve)} \\ \hline \end{array} \] The correct answer is

• A. A-III, B-I, C-IV, D-II
• B. A-IV, B-III, C-II, D-I
• C. A-IV, B-III, C-I, D-II
• D. A-III, B-IV, C-I, D-II

Hint:

Transition elements often show anomalous similarities due to poor shielding by \(d\)-electrons. Noble gases usually possess positive electron gain enthalpy because additional electrons must enter higher energy orbitals.

Answer 1

The Correct Option is D

Step 1: Understand a matching question.
Each pair of elements in List-I shares one periodic property listed in List-II. We compare each pair and decide which property they have almost the same.
Step 2: Match Co and Ni.
Cobalt and nickel are next to each other in the transition series. Because $3d$ electrons shield poorly, their metallic radii come out almost equal. So Co, Ni go with metallic radius, that is $A \rightarrow III$.
Step 3: Match K and Ba.
Potassium and barium are both very reactive metals that lose electrons easily. They have similarly large negative standard reduction potentials. So K, Ba go with standard reduction potential, that is $B \rightarrow IV$.
Step 4: Match N and Cl.
Nitrogen and chlorine both have an electronegativity close to $3.0$ on the Pauling scale. So they share electronegativity, that is $C \rightarrow I$.
Step 5: Match Ar and Kr.
Argon and krypton are noble gases with full shells. They resist gaining electrons, so both have similar (positive) electron gain enthalpy. So Ar, Kr go with electron gain enthalpy, that is $D \rightarrow II$.
Step 6: Write the full match.
Combining all pairs gives \[ \boxed{A-III,\ B-IV,\ C-I,\ D-II} \]