Q.What do you expect the nature of hydrides is, if formed by elements of atomic numbers 15, 19, 23 and 44 with dihydrogen? Compare their behaviour towards water.

Identify each element by its atomic number:

• Z = 15 → Phosphorus (P), a p-block non-metal of group 15. It forms a covalent (molecular) hydride, PH3 (phosphine), an electron-rich hydride analogous to NH3. PH3 is molecular and largely unreactive/stable towards water (it does not hydrolyse readily).

• Z = 19 → Potassium (K), an s-block alkali metal (group 1). It forms an ionic (saline) hydride, KH, containing discrete K⁺ and H⁻ ions. KH reacts violently with water, being strongly basic/reducing:

• Z = 23 → Vanadium (V), a d-block transition metal. It forms a metallic (interstitial), non-stoichiometric hydride ($VH_x$), where hydrogen occupies interstitial sites in the metal lattice. Such hydrides are essentially inert/unreactive towards water, retaining the metal's characteristic stability.

• Z = 44 → Ruthenium (Ru), also a d-block transition metal. Like V, it (if it forms a hydride at all under the relevant conditions) would give a metallic/interstitial-type hydride, likewise essentially unreactive with water. …

Identify each element from its atomic number and periodic block (p-block, s-block, d-block), predict the hydride type accordingly (covalent, ionic, metallic), and …

• Misidentifying the elements from their atomic numbers — double-check P=15, K=19, V=23, Ru=44 against the periodic table. …