Question Analysis: Assertion (A) and Reason (R) type question.

Step 1 (Governing Principle): [0.25 Mark]

The principle of Charge Neutrality in semiconductors states that the total number of positive charges (protons) must equal the total number of negative charges (electrons) within the crystal lattice of a doped semiconductor, provided no external charge is added.

Step 2 (Step-by-Step Logical Deduction): [0.50 Mark]

• The intrinsic semiconductor (e.g., Silicon) is electrically neutral.
• The pentavalent impurity atom (e.g., Phosphorus) is also electrically neutral before doping.
• When the impurity atom is incorporated into the lattice, it shares 4 valence electrons with neighboring atoms. The 5th electron becomes a free charge carrier ($e^-$).
• The impurity atom becomes a positive ion ($D^+$) fixed in the lattice.
• The total charge $Q_{total}$ of the n-type crystal is: $$Q_{total} = \sum q_{protons} + \sum q_{electrons} + \sum q_{ions} = 0$$
• Since the number of added electrons equals the number of positive donor ions, the net charge remains zero.

Step 3 (Final Concluded Answer): [0.25 Mark]

Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).

💡 EL10 Concept Insight: Think of it like a group of people where everyone is neutral; even if one person gives away a "gift" (the electron) to the group, that person becomes a "positive" giver, but the total group balance stays exactly at zero because the gift is still inside the room!