Step 1: Understanding the Concept:
Equivalent weight for acids is $M/\text{basicity}$, and for salts, it is $M/\text{total positive charge on cation}$.
Step 2: Key Formula or Approach:
Calculate Molecular Weight ($M$) and divide by n-factor ($n$) for each:
Step 3: Detailed Explanation:
\begin{enumerate}
Sulphuric acid ($H_2SO_4$): $M = 98, n = 2 \implies Eq. wt = 49$.
Sodium carbonate ($Na_2CO_3$): $M = 106, n = 2 \implies Eq. wt = 53$.
Sodium sulphate ($Na_2SO_4$): $M = (23 \times 2) + 32 + (16 \times 4) = 46 + 32 + 64 = 142$. $n = 2 \implies Eq. wt = 71$.
Calcium carbonate ($CaCO_3$): $M = 100, n = 2 \implies Eq. wt = 50$.
\end{enumerate}
Step 4: Final Answer:
Sodium sulphate has the highest equivalent weight (71).