H is less electronegative than carbon and F is more electronegative than carbon and thus Hydrogen has positive charge and Flourine has negative charge.

The oxidation state of H = +1

Oxidation state of F = -1

Let the oxidation state of C = 'x'

Since the molecule is neutral, the net charge is zero. Therefore,

1(x)+2(1)+2(-1)= 0

x = 0

Therefore, the oxidation state of Carbon is zero.