Which of the following is NOT correct about hydrides? I. Saline hydrides are stoichiometric and metallic hydrides are non-stoichiometric II. BeH ₂ is monomeric whereas MgH ₂ is polymeric III. Hydrides of the elements of Group 13 are electron deficient and those of Group15 are electron rich IV. NaH reacts with water and liberates H ₂ whereas B ₂ H ₆ does not react with water