When a glass rod is rubbed with a silk cloth, electrons are removed from the glass rod. This process is known as charging by friction or triboelectric charging. Let's understand this phenomenon in detail.

What is triboelectric charging?
Triboelectric charging is a process in which two objects become electrically charged after coming into contact and then separating. When two materials with different tendencies to attract or release electrons come into contact and are then separated, one material tends to gain electrons (becoming negatively charged) while the other material tends to lose electrons (becoming positively charged). This happens due to the difference in the electronegativity of the materials involved.

Process of rubbing glass rod with silk cloth:
When a glass rod is rubbed with a silk cloth, the atoms in the glass rod and the silk cloth interact with each other. The glass rod has a higher tendency to release electrons, while the silk cloth has a higher tendency to attract electrons. As the glass rod and silk cloth come into contact and are rubbed together, the electrons from the glass rod are transferred to the silk cloth.

Explanation of the answer:
The correct answer to the given question is option 'b' - electrons are removed from the glass rod. When the glass rod is rubbed with the silk cloth, the glass rod loses electrons, which results in a positive charge on the glass rod. The silk cloth gains these electrons, acquiring a negative charge. This transfer of electrons from the glass rod to the silk cloth leads to the separation of charges and the creation of an electrically charged glass rod and silk cloth.

Key Points:
- Rubbing a glass rod with a silk cloth results in triboelectric charging.
- The glass rod loses electrons during the rubbing process.
- The silk cloth gains electrons during the rubbing process.
- The glass rod becomes positively charged after losing electrons.
- The silk cloth becomes negatively charged after gaining electrons.

Overall, when a glass rod is rubbed with a silk cloth, electrons are removed from the glass rod, resulting in a positively charged glass rod and a negatively charged silk cloth.