Sodium in water catches fire due to formation of;

When the sodium atom is forced to react with the water, sodium ions and hydroxyl ions are created along with the release of the gas, and this reaction is exothermic in nature, meaning that heat is produced. Sodium is an s-block element that is an alkali metal with an atomic number of 11, and a mass number of 23. It possesses one electron in its outermost shell and a strong tendency to shed the electron in order to obtain the stable electronic configuration of the closest noble gas, namely neon. It is extremely soft and could be readily sliced with a knife.

In the reaction of sodium with water sodium and hydroxide ions, hydrogen and heat are produced.

$2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{Na}}^{+}+2{\mathrm{OH}}^{-}+{\mathrm{H}}_2+∆$

Since hydrogen is flammable it easily catches fire due to the evolution of heat.

Hence, option D is correct.