Correct Option
The correct option is (a).
Explanation
The concept of electric charge is based on the triboelectric effect (charging by friction) and the fundamental laws of electrostatics. Historically, Benjamin Franklin established the convention for naming charges as "positive" and "negative" based on specific material interactions.
Statement-wise Analysis
- Statement 1 is Correct: According to the standard convention of electrostatics, when a glass rod is rubbed with silk, the glass rod loses electrons and acquires a positive charge. The silk cloth, gaining electrons, acquires a negative charge.
- Statement 2 is Incorrect: When a plastic straw (or rod) is rubbed with polythene (or fur), the plastic typically gains electrons due to its position in the triboelectric series. Consequently, the plastic acquires a negative charge, not a positive one.
- Statement 3 is Incorrect: A fundamental property of electric charges is that like charges repel (positive-positive or negative-negative) and unlike charges attract (positive-negative). Therefore, positive and negative charges attract each other, they do not repel.
Key Takeaway: By convention, a glass rod rubbed with silk is positively charged, while a plastic rod rubbed with fur is negatively charged. Fundamentally, like charges repel and unlike charges attract.