How many effective pairs are in I2, O2 and HF? Why?

for I2 I thought it was 1 for both but apparently it is 4 effective pairs and 1 effective bond and for O2 I thought it was 1 for both, but it was corrected to 3 effective pairs and 1 effective bond. For HF I thought it was 1 for both but my teacher said 4 effective pairs and 1 effective bond. I don't know how to get the correct answer.