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

Solution

Chemistry ma’am · 3 steps

Two checks: is it liquid at 100 °C, and does it leave water alone? Only gallium passes both.

1. What liquid needs. Pure water boils at 100 °C. To stay liquid there, an element must melt below 100 °C and boil well above it. It must also not react with the water.

   Element	Melting point	Boiling point	In boiling water
   Li	181 °C	1342 °C	still solid, and reacts to give LiOH + H₂
   Br	-7 °C	59 °C	already past its boiling point, so it is a gas
   Cs	28 °C	671 °C	molten, but reacts explosively with water
   Ga	30 °C	about 2400 °C	liquid, and unreactive towards pure water

2. Why gallium is special. Gallium has an unusually low melting point but a very high boiling point. That gives it one of the widest liquid ranges of any element. A thin oxide film also protects it, so pure water does not attack it.
3. So. Only gallium stays as a liquid inside boiling water, so the answer is (d).

The idea to keep. Gallium melts in your palm at about 30 °C yet boils near 2400 °C. That huge liquid range makes it the go-to answer whenever a question asks what stays liquid over a wide temperature range.

Answer from the NTA final answer key. Solution by PrepWiser.