Match semiconductor elements and dopants to their properties: (A) Silicon, (B) Arsenic, (C) Indium, (D) Germanium — with: (1) is trivalent (acceptor), (2) rarely used as a semiconductor today, (3) is pentavalent (donor), (4) intrinsic semiconductor (classic base material).

Introduction / Context:
Doping changes the electrical behavior of semiconductors by introducing donors or acceptors. This question ties each listed element to its typical role or property in semiconductor technology.

Given Data / Assumptions:

• Silicon (Si) and Germanium (Ge) are group-IV base semiconductors.
• Arsenic (As) is a group-V donor; Indium (In) is a group-III acceptor.
• Contemporary mainstream devices overwhelmingly use silicon; germanium is comparatively rare in bulk devices (though present in specialized heterostructures).

Concept / Approach:
Map periodic-table group to doping role: group-V → pentavalent donor (n-type); group-III → trivalent acceptor (p-type). Silicon is the canonical intrinsic substrate material in teaching contexts; germanium is much less common today in mass production.

Step-by-Step Solution:

Verification / Alternative check:
Group mapping: Si/Ge are group 14; As is group 15 (donor); In is group 13 (acceptor). Historical usage shows a move from Ge to Si for thermal stability and oxide quality.

Why Other Options Are Wrong:

• A-1, B-2, C-3, D-4: Mislabels silicon and germanium roles and swaps dopant valences.
• A-4, B-3, C-2, D-1: Puts Indium as 'rarely used as a semiconductor,' which is inaccurate for its dopant role.
• A-2, B-1, C-3, D-4: Reverses donor/acceptor assignments.

Common Pitfalls:

• Confusing 'intrinsic' (pure material) with 'p-type' or 'n-type' (doped).
• Thinking germanium is equally common today; it is niche compared to silicon.

Final Answer:
A-4, B-3, C-1, D-2