Which of the following is NOT correct about hydrides?
I. Saline hydrides are stoichiometric and metallic hydrides are non-stoichiometric.
II. $$\text{BeH}_2$$ is monomeric whereas $$\text{MgH}_2$$ is polymeric.
III. Hydrides of the elements of Group 13 are electron deficient and those of Group 15 are electron rich.
IV. NaH reacts with water and liberates $$\text{H}_2$$ whereas $$\text{B}_2\text{H}_6$$ does not react with water.