SiF4 on Hydrolysis gives X and Y.  SiCl4 on Hydrolysis gives X and Z covalency of central atom in Y is C1 and that of Halogen in Z is C2. Then C1+C2 is

When silicon tetrafluoride under goes Hydorlysis gives metasilic acid and Hydrogen Hexafluoro silicate(IV)SiF4+H2O→H2SiO3+H2SiF6 SiCl4+4H2O→H4SiO4+4HCl ∴Covalency central atom in (Y) H2SiF6is ‘6’ covalency of Chlorine in HCl is ‘1’∴C1+C2=6+1=7