Write the structure of pyrophosphoric acid.

In the preparation of H₂SO₄ by Contact Process, why is SO₃ not absorbed directly in water to form H₂SO₄?

Write a balanced chemical equation for the reaction showing catalytic oxidation of NH₃ by atmospheric oxygen.

PH₃ forms bubbles when passed slowly in water but NH₃ dissolves. Explain why?

In PCl₅, phosphorus is in sp³d hybridised state but all its five bonds are not equivalent. Justify your answer with reason.