In qualitative analysis when H₂S is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. HNO3, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________. 

(i) Deep blue precipitate of Cu(OH)₂

(ii) Deep blue solution of [Cu(NH₃)₄]²⁺ 

(iii) Deep blue solution of Cu(NO₃)₂

(iv) Deep blue solution of Cu(OH)₂ .Cu(NO₃)₂

HClO₄ is the most acidic compound.

Group number = 11 (Atomic number = 111)

Heavier element of p block do not from pπ− pπ bonds as their atomic orbital are so large and diffius that they cannot have effecitve overlapping.

The inertness of ? subshell electrons towards bond formation is known as inert pair effect. This effect increases down the group thus, for Sn,  oxidation state is more stable, whereas, for Pb,  oxidation state is more stable, i.e.,  is reducing while  is oxidising.