Q.Which of the following compounds will not evolve H₂ gas on reaction with alkali metals ?

Sodium metal is stored under kerosene (a hydrocarbon liquid) to protect it from reacting with moisture and oxygen in air.

Sodium is a soft, highly reactive alkali metal. It reacts vigorously and exothermically with water:

2Na + 2H2O -> 2NaOH + H2 (the reaction can even ignite the liberated hydrogen)

It also readily reacts with atmospheric oxygen and moisture if left exposed, tarnishing and eventually catching fire. To prevent contact with air and water, freshly cut sodium is stored fully immersed in kerosene (a non-polar hydrocarbon liquid) in which sodium does not dissolve or react, so it stays protected while remaining easy to retrieve for use.

Storing it in water (option a) or alcohol (option c) would cause an immediate vigorous/exothermic reaction (sodium reacts with alcohol too, releasing hydrogen, though more slowly than with water), so both are unsafe/incorrect.

Sodium metal is stored under kerosene because kerosene is chemically inert to sodium and excludes atmospheric oxygen and moisture, both of which react with sodium.

Sodium is a soft, highly reactive alkali metal. It reacts readily with:

• Oxygen in air, forming a layer of sodium oxide/peroxide (tarnishing and eventually corroding the metal).
• Moisture (water vapour), reacting vigorously (even violently) to form sodium hydroxide and hydrogen gas: 2Na + 2H2O -> 2NaOH + H2.

Because of this reactivity, freshly cut sodium (which shows a shiny metallic surface) must be protected from air and water. Kerosene is a non-polar hydrocarbon liquid that does not react with sodium and forms a physical barrier that keeps oxygen and moisture away from the metal's surface, so sodium is stored fully immersed in kerosene. Water itself cannot be used (option d) since sodium reacts violently with it; alcohol (b) and ether (c) also react with or are unsuitable for storing reactive metals.