Which of the following molecules(s) is /are having `p pi -dpi` back bonding

The molecule in which an atom is associated with more than 8 electrons is known as hypervalent molecule and less than 8 electrons is known as hypovalent molecule. All hypervalent molecules must have ppi-dpi bonding but the molecules having back bonding back boding need not to have always ppi-dpi bondin. Q.Which of the following molecule is not having ppi-dpi bonding:

The molecule in which an atom is associated with more than 8 electrons is known as hypervalent molecule and less than 8 electrons is known as hypovalent molecule. All hypervalent molecules must have ppi-dpi bonding but the molecules having back bonding back boding need not to have always ppi-dpi bondin. Q.Which of the following molecule is not having ppi-dpi bonding:

Which of the following molecules have a dative bonding (p pi-d pi) ?

Which of the following molecules involves the formation of dpi - p pi bonding ?

Which of the following molecules involves the formation of dpi - p pi bonding ?