Think of washing soda like a 'chemical eraser' that grabs onto the minerals causing hardness in your water, preventing them from ruining the cleaning power of your soap.

P-G-S-T: Paper, Glass, Soap, Textiles — these are the primary industries where $Na_2CO_3$ is a vital reagent.

Washing soda acts as a chemical pulping and bleaching aid in the paper industry, helping to break down lignin and maintain the alkaline pH necessary for the processing of wood pulp. It is also an effective softening agent because it reacts with calcium and magnesium ions in hard water to form insoluble carbonate precipitates, thereby softening the water. The reaction for removing permanent hardness (caused by $CaCl_2$) is: $Na_2CO_3 + CaCl_2 \rightarrow CaCO_3(s) + 2NaCl$

When answering 'INCORRECT' questions, identify the three clearly true statements first to isolate the outlier, which is often a false claim about industrial applications.