Which one of the following elements will remain as liquid inside pure boiling water?

🧠 For an element to stay liquid in boiling water, it needs MP below 100 °C, BP above 100 °C, AND no reaction with water Boiling water is at $100\,°\text{C}$. So you need a melting point below that (so it is melted) AND a boiling point above that (so it has not vaporized) AND chemical inertness towards water (otherwise it dissolves or reacts).

🗺️ Eliminate each option Br: BP $= 59\,°\text{C}$. At 100 °C it would already be vapor, not liquid. Reject. Li: MP $= 180\,°\text{C}$ — still solid at 100 °C. Plus Li reacts vigorously with water. Reject. Cs: MP $= 28.5\,°\text{C}$ — but Cs explodes on contact with water. Reject. Ga: MP $\approx 30\,°\text{C}$, BP $\approx 2204\,°\text{C}$, and Ga does not react with water under normal conditions. Inside boiling water, Ga is a calm shiny liquid pool.

⚠️ The trap Cs looks tempting because of its low melting point ($28.5\,°\text{C}$). But Cs is the most reactive alkali metal — it would never sit calmly in water. The "doesn't react" condition is just as important as the melting point. Ga is the famous safe-with-water low-MP metal.

$\boxed{\text{Answer: (a)}}$