Name one metal with following properties: A metal that floats on water, reacts with it, and forms an alkali.

Lithium, sodium, and other Group 1 metals have low densities and float in water. The other two heavy metals, such as rubidium and cesium, are more denser, and as a result, they float on water.
Due to their reaction with atmospheric oxygen, they are often preserved as mineral oil. When these metals are combined with water, they all undergo an exothermic process that results in the production of hydrogen.  Group one metals being very less dense (low mass) floats in water. In the given options sodium and lead are group one or alkali metals. Lead does not react with water. The remaining option sodium reacts with water and produces a basic sodium hydroxide as follows;

$2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{NaOH}+{\mathrm{H}}_2$

Hence, option 2 is correct.