When a potential difference is put across a wire, ___.

a. electron speeds decrease

b. electrons drift slowly toward the positive end of the wire

c. conduction of electricity ceases

d. electron energy lessens

option (b)

Explanation:

As the potential difference is applied accros a wire, the electron drifts slowly towards the positive end of the wire as the electrons are negatively charged so they attract towards the positive end.

b. electrons drift slowly toward the positive end of the wire

Explanation:

Motion of electrons constitutes current. According to Ohm's law, the current in the wire is directly proportional to the potential difference across the two ends of the wire.

I ∝ V

⇒V = I R

When potential difference is put, the electrons towards the positive end. Thus, option b is correct.