Sodium salt of higher molecular weight fatty acid is termed as the __________ soap.

Sodium salts of higher molecular weight fatty acids are commonly known as hard soaps.
These soaps are formed when a fat or oil is treated with sodium hydroxide (NaOH) during the saponification process.

The sodium salts produced are solid in nature and have a relatively high melting point.
They are called hard soaps because they are less soluble in water and are typically used for washing and cleaning purposes.

In contrast, when potassium hydroxide (KOH) is used instead of NaOH, the resulting potassium salts of fatty acids are soft soaps, which are more soluble in water.

Hence, the sodium salt of higher molecular weight fatty acid is termed as the hard soap.