The chemical formula of borax is __________.

The correct answer is option 2. \(Na_2B_4O_7.10H_2O\).

Borax, also known as sodium borate, is a compound with the chemical formula \(Na_2B_4O_7 \cdot 10H_2O\). Let's break down the components of this formula.

1. \(Na_2\): This represents two sodium ions.

2. \(B_4O_7\): This represents the tetraborate anion, which consists of four boron atoms and seven oxygen atoms.

3. \(10H_2O\): This indicates ten water molecules, which are part of the crystal structure as water of crystallization.

The combination of these elements results in borax. It is a white crystalline powder that dissolves in water, and it is often used in various applications, including as a cleaning agent, a flux in metallurgy, and a component in some cosmetics and household products. The water molecules in the formula are loosely bound and can be driven off by heating, leaving anhydrous borax under certain conditions.