Consider the follawing species
\( O \left( CH _{3}\right)_{2}, N \left( SiH _{3}\right)_{3}, CO , O \left( SiH _{3}\right)_{2},: CCl _{2}(\sin g l e t), CCl _{3}, Si ( OH )_{4}, OCl _{2} \) and \( MeNCS \).
If \( x \) is the total no of species having \( ( P \pi- P \pi) \) back bonding, \( y \) is the no. of species having \( P \pi- d \pi \) back bonding and \( z \) is the no of species having no back bonding then find the value of \( (x+y-z) \) ?