KI solution + starch + solution of salt 'X' $\to$ Deep blue solution 'X' is/ are :

Potassium iodide and iodine solutions produce complex iodide ions, which are soluble in water but change colour when starches are present. This is because the complex iodide ions become entangled in the spirals of the starch polymer chains, forcing them to become linear and alter their electron arrangement.

KI solution + starch + solution of salt ${\mathrm{NaNO}}_2$ deep blue solution ${\mathrm{NaNO}}_2$

KI solution + starch + solution of salt $\mathrm{Ba}{\left({\mathrm{MnO}}_4\right)}_2-$ deep blue solution $\mathrm{Ba}{\left({\mathrm{MnO}}_4\right)}_2$.

KI solution + starch + solution of salt ${\mathrm{FeCl}}_3-$  deep blue solution ${\mathrm{FeCl}}_3$.

Thus, option b, c and d are correct.