Which of the following is NOT a use of washing soda?

It is used to make drinking water free from germs.

The correct answer is option 3. It is used to make drinking water free from germs.

The use of washing soda listed that is NOT correct is It is used to make drinking water free from germs.

Washing soda, also known as sodium carbonate \((Na_2CO_3)\), is primarily used in domestic cleaning agents, in industries such as glass, soap, and paper manufacturing, and for removing permanent hardness of water. It is not typically used to make drinking water free from germs. Instead, other substances like chlorine-based compounds or UV treatment are more commonly used for disinfecting drinking water.