What is an alkali metal with fewer than 10 protons in its nucleus?

Lithium

Explanation:

Alkali metals are group of metals which are present in first group of periodic table. As we know atomic number is equal to number of protons contained by a particular element. Therefore, the alkali metals along with there number of protons are listed below;

Alkali Metal Number of Protons

Lithium 3

Sodium 11

Potassium 19

Rubidium 37

Cesium 55

Francium 87

Hence, it is cleared from above table that Lithium is having fewer protons than 10.