Hint: Ions conduct electricity in an aqueous solution

Metallic hydrides are also known as Non-stoichiometric (or Interstitial ) Hydrides. They are almost always non-stoichiometric, being deficient in hydrogen.

For example, LaH_2.87, YbH_2.55, TiH_1.5–1.8, ZrH_1.3–1.75, VH_0.56, NiH_0.6–0.7, PdH_0.6–0.8 etc. Thus, the first statement is correct. 

Metallic hydrides conduct heat and electricity though not as efficiently as their parent metals do. Thus, the second statement is also correct.

The ionic hydrides are crystalline, non-volatile, and non-conducting in solid-state. However, their melts conduct electricity and on electrolysis liberate dihydrogen gas at the anode, which confirms the existence of H^– ion. Thus, the third statement is correct.