Correct Answer - C
( c) The octete of all atoms are complete in structures `a` and `b` The molecule in which all the atoms have complete octet is more stable than the atom having incomplete octet. Larger the number of resonating structures, larger will be the stability. Thus, structures `a` and `b` are stable.
Instructure `(d)`, the electron deficiency of positive charged carbon is duly compensated by lone pair electrons of adjacent oxygen atoms, while such neihbour group support is not available in structure `(c)`. Hence, structure `(c)` is less stable in comparion to structure `(d)`.
