Which alkali metal hydroxide gives the oxide when heated strongly, 2MOH -> M2O + H2O, at a moderate temperature while the others are stable?

JEE Main levelSingle correct optionDifficulty 2 of 3sb130

Which alkali metal hydroxide gives the oxide when heated strongly, $2 MOH M X_{2} O + H X_{2} O$ , at a moderate temperature while the others are stable?

The small

Li X^{+}

ion gives an oxide of very high lattice energy, which favours loss of water:

2 LiOH Li X_{2} O + H X_{2} O

. The hydroxides of Na, K and Cs volatilise or melt without decomposing at comparable temperatures.