The formation of ammonium ion (NH₄⁺) from NH₃ and H⁺ involves: MCQ with Answer and Explanation

Explanation:
A molecule is the smallest particle of a compound (or element) that can exist independently and exhibit the compound's chemical properties. For covalent compounds (water, CO₂), the molecule is the discrete particle. For ionic compounds, the term 'formula unit' is used rather than molecule. Atoms are smallest particles of elements. Ions are charged atoms/molecules.

Explanation:
Ammonium chloride (NH₄Cl) sublimes on heating—it directly converts from solid to vapor without passing through the liquid phase—while common salt (NaCl) remains as a solid residue. This property allows separation by sublimation. Filtration would not work because both are soluble in water, distillation is for liquids, and chromatography separates dissolved substances based on differential adsorption. Lab tip: NH₄Cl vapors condense on the cool funnel to give solid sublimate.

Explanation:
Magnesium reacts with hot water or steam to form MgO/Mg(OH)₂ and H₂, but very slowly with cold water (thin layer of insoluble hydroxide inhibits reaction). Sodium, potassium, and calcium react vigorously with cold water. Aluminium, zinc, iron react with steam but not cold water. Reactivity with water follows the series: K, Na, Ca (cold water); Mg, Al, Zn, Fe (steam).