How do you add the reviewing toolbar if it does not appear by default when you turn on track changes?

The two main features of the Reviewing Toolbar (RT) are the "Comment" and "Track Change" feature. With these, you can make comments and changes to a document, and then give the reader the option of accepting or rejecting them.
Using the RT  is the most economical way to edit a document. If it is does not appear by default you can turn it on.
There are three possible ways how to do that:

1. View>Toolbar>Reviewing
2. Right click on any Toolbar> Reviewing
3. Double click on TRK  in the Status Bar 

answer: when the substance contain the two parts (polar and non-polar) like soap.

explanation:

soap is produced from the basic hydrolysis of ester "saponification", it is considered as a salt of hydrocarbons. the soap molecule contains the two parts: a polar group   (-coo-na+) and a non-polar group (r-hydrocarbon part). the polar group is called the head and the tail is the non-polar group. the polar group is hydrophilic in nature (water loving) and the non-polar group is hydrophobic in nature (water repelling).the polar/non-polar nature of a substance is useful that it can dissolve the non-polar substances by the polar part and also can dissolve the polar substances by the non-polar part. it commonly used in detergents and soaps.