Question

Name one metal which fit each of the following:
A metal that floats on water, reacts with it, and forms an alkali.

Answer 1

Hint: We should be having an idea about the requirements for a metal to float on water, reacting to water and then forming an alkali. For floating in water the metal should be having low density. There are various examples of such metals, we need to write any one among them.

Step by step answer:
The Group 1 metals such as Lithium, Sodium and Potassium have low densities and float in water. However, the other two heavy metals like Rubidium and Caesium are very denser and so they sink in water.
They are normally stored as mineral oil because they react with oxygen that is present in the air.
When these metals are added to the water, they all react vigorously producing hydrogen in an exothermic reaction. The further down the group we go, the more vigorous the reaction becomes.
For the answer we will consider the example of Sodium. Sodium floats on water. It is highly reactive. When it is in water, it reacts with water instantly and vigorously resulting in the formation of caustic soda and hydrogen gas.
The reaction of sodium in water is given below:
$\text{2Na + 2}{\text{H}}_{\text{2}}\text{O }\stackrel{}{\to }\text{ 2NaOH + }{\text{H}}_{\text{2}}\text{(g)}$
Sodium reacts with water to form a colourless solution of sodium hydroxide (NaOH) and hydrogen gas (${\text{H}}_{\text{2}}$). The resulting solution is basic because of the dissolved hydroxide. During the reaction, the sodium metal may well become so hot that it can catch fire and burn with a characteristic orange colour.

Note: The tendency of sodium to get rid of the electron, coupled with the ability of the oxygen atom in water to accept that electron leads to an explosive reaction. This reaction releases a lot of energy in the form of heat.