Consider the following cases :

(a) $\mathrm{CaSO}_4 + \mathrm{Al} \longrightarrow$

(b) $\mathrm{CuSO}_4 + \mathrm{Ca} \longrightarrow$

(c) $\mathrm{FeSO}_4 + \mathrm{Cu} \longrightarrow$

(d) $\mathrm{ZnSO}_4 + \mathrm{Mg} \longrightarrow$

The cases in which new products will form are -

A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution. According to the reactivity series given in Table 3.2 of the NCERT text, the order of reactivity is:

$$\mathrm{Ca} > \mathrm{Mg} > \mathrm{Al} > \mathrm{Zn} > \mathrm{Fe} > \mathrm{Cu}$$

Let's analyze each case:

• (a) $\mathrm{CaSO}_4 + \mathrm{Al}$: Since Calcium ($\mathrm{Ca}$) is more reactive than Aluminium ($\mathrm{Al}$), aluminium cannot displace calcium. No reaction occurs.
• (b) $\mathrm{CuSO}_4 + \mathrm{Ca}$: Since Calcium ($\mathrm{Ca}$) is more reactive than Copper ($\mathrm{Cu}$), calcium will displace copper to form calcium sulphate and copper. A reaction occurs:

$$\mathrm{CuSO}_4(aq) + \mathrm{Ca}(s) \rightarrow \mathrm{CaSO}_4(aq) + \mathrm{Cu}(s)$$

• (c) $\mathrm{FeSO}_4 + \mathrm{Cu}$: Since Iron ($\mathrm{Fe}$) is more reactive than Copper ($\mathrm{Cu}$), copper cannot displace iron. No reaction occurs.
• (d) $\mathrm{ZnSO}_4 + \mathrm{Mg}$: Since Magnesium ($\mathrm{Mg}$) is more reactive than Zinc ($\mathrm{Zn}$), magnesium will displace zinc to form magnesium sulphate and zinc. A reaction occurs:

$$\mathrm{ZnSO}_4(aq) + \mathrm{Mg}(s) \rightarrow \mathrm{MgSO}_4(aq) + \mathrm{Zn}(s)$$

Therefore, new products will form in cases (b) and (d).

• Option A is incorrect because case (a) does not yield any reaction.
• Option B and Option C are incorrect because case (c) does not yield any reaction.