How does a rubber rod become negatively charged through friction?
a: it touches a negatively charged object, and protons move off of the rod.
b: it touches a positively charged object, and electrons move onto the rod.
c: it is rubbed with another object, and electrons move onto the rod.
d: it is rubbed with another object, and protons move off of the rod.

The correct answer to the question is C) It is rubbed with another object, and electrons move onto the rod.

EXPLANATION:

Before going to answer this question, first we have to understand the charging by friction.

Charging by friction is one mode of charging a body by rubbing it with another body in which there will be actual transfer of electrons from one body to another body.

In this process, the electrons will be transferred from a low affinity body to a high affinity body. The high electron affinity body will be negatively charged as it accepts electron, and the low electron affinity body will be positively charged.

As per the question, the charge of rubber rod is negative. Hence, it must have rubbed with another object, and electrons move onto the rod.

The protons can not move onto the rod as protons are bound to the nuclei of atoms.