JEE Main Test 85

Hydration of ions is the interaction between the ions and water molecules or other polar solvents. The negative side of a dipolar water molecules attracts and is attracted by any positive ion in solution. Because of this ion – dipole force water molecules cluster around the positive ions occurs. Similarly +ve end of water molecules are attracted to negative ions. Therefore hydration of ions aqueous solution is an example of ion – dipole interaction.

Polarizing power of cation α charge/size, for Be²⁺, Mg²⁺, Ca²⁺ since charge is same and size is in the order Ca²⁺> Mg²⁺> Be²⁺, the order of polarizing power is

Be²⁺> Mg²⁺> Ca²⁺, charge of K⁺ is lowest and size is larger than Ca²⁺.

∴ its polarizing power is lowest.

Hence the correct order is K⁺> Ca²⁺> Mg²⁺> Be²⁺.

The angles around central atom H – M – H decreases from NH₃ to SbH₃ as,

This variation in bond angle can be explained on the basis of electronegativity of the central atom. Since nitrogen atom is highly electronegative. So in NH₃ there is high electron density around the N – atom which cause greater repulsion between the electron pairs around the N – atom resulting in maximum bond angle. Since electronegativity decreases down the group, the electron density also decreases and consequently the repulsive interactions between the electron pairs also decreases there by decreasing the bond angle H – M – H.

∴ The order is NH₃> PH₃> AsH₃> SbH₃