Which of the following must be true in order for an object to stay in place?
the forces must be balanced.
the forces must be positive.
the forces must be negative.
the forces must be gravitational.

The forces must be balanced.

This is in accordance to Newton's first law of motion, which states that an object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an unbalanced force.
An unbalanced force is also known as a resultant force.

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.