Determine the oxidation number of: (i) Si in SiH₄ (ii) B in BH₃ (iii) B in BF₃. 

(i) Let the oxidation number of Si = x
Writing the oxidation number of each atom at the op of its symbol,
  x               -1
Si                H₄
The algebraic sum of oxidation number of various atoms = 0
x + 4 (-1) = 0
     x  = 4
(ii) Let the oxidation number of B =x
Writing the oxidation number of each atom at the top of its symbol
x               -1
B               H₃
The algebraic sum of the oxidation number of various atoms = 0
        x  + 3(-1) = 0
                    x = 3
(iii) Let the oxidation number of B = x
Writing the oxidation number of each atom at the top of its symbol,
 x      -1 
B        F₃
The algebraic sum of the oxidation number of various atoms = 0
                    x +  3 (-1) = 0
                                x = 3