In p-type silicon at room temperature, the acceptor atoms

The correct answer is Option (4) → become negative ions fixed in the lattice

An acceptor atom completes its fourth bond with an electron taken from a neighbouring bond. A hole is left where that electron came from.

Option (1) become positive ions fixed in the lattice — Incorrect. The acceptor gains an electron, so its charge becomes negative. A fixed positive ion is what an ionised donor forms in n-type material.

Option (2) remain electrically neutral, since each one just takes the place of a silicon atom — Incorrect. The trivalent atom holds the extra electron it shares with its fourth neighbour. So it becomes negatively charged. The crystal as a whole stays neutral. Each such negative charge is balanced by the hole that goes with it.

Option (3) become negative ions that move through the crystal and carry current — Incorrect. The ion is bonded to the surrounding silicon atoms and stays at its site. The current in p-type silicon is carried mainly by the holes.

Option (4) become negative ions fixed in the lattice — Correct. After taking the extra electron, each acceptor is a core of one negative charge, along with its hole. Its bonds hold it in place.

NCERT (2026-27):
Extrinsic Semiconductor – “… Note that the trivalent foreign atom becomes effectively negatively charged when it shares fourth electron with neighbouring Si atom. Therefore, the dopant atom of p-type material can be treated as core of one negative charge along with its associated hole ….”

p-n Junction Formation – “Similarly, when a hole diffuses from p → n due to the concentration gradient, it leaves behind an ionised acceptor (negative charge) which is immobile.”