Which of the following is a tetrabasic acid?

Which one of the orders is correctly matched with the property mentioned against it?

$P_2O_5$ is heated with water to give:

$NH_3$ reacts with bleaching powder to give:

Which of the following statements is $NOT$ correct?

$A$ group $15$ element forms $d \pi - d \pi$ bond with transition metals. It also forms a hydride,which is the strongest base among the hydrides of other group members that form $d \pi - d \pi$ bonds. The atomic number of the element is $.......$