In atmospheric electricity, lightning is produced mainly when which of the following situations occurs between clouds and the surrounding air?

Introduction / Context:
Lightning is one of the most dramatic phenomena in atmospheric electricity. During thunderstorms, huge electric charges build up in clouds and between clouds and the ground. Eventually, the electric field becomes strong enough to cause a sudden discharge, which we see as a lightning flash. This question tests your understanding of the physical condition that triggers lightning in terms of electric charges and the breakdown of air as an insulator.

Given Data / Assumptions:
- We are dealing with lightning in the atmosphere, not small laboratory discharges.
- Options describe different qualitative explanations involving charges, friction and water vapour.
- We assume the standard scientific explanation of lightning due to electric field breakdown of air between regions of opposite charge.

Concept / Approach:
Air is usually a good insulator, but when the electric field between two regions of opposite charge becomes very strong, it can ionise air molecules. This ionisation creates a conducting path, allowing a sudden flow of charge or electric discharge. In thunderstorms, strong opposite charges can accumulate in different parts of a cloud or between a cloud and the earth. When the electric field exceeds a critical value, the insulating property of air breaks down, and lightning occurs. It is not caused mainly by similar charges rushing together, nor by friction with impurities, nor simply by water vapour generating electricity by itself.

Step-by-Step Solution:
Step 1: Recall that lightning requires very large electric potential differences between regions in the atmosphere. Step 2: Understand that opposite charges in different regions (such as cloud top and bottom or cloud and ground) create strong electric fields. Step 3: As the field grows, air molecules become ionised, and the insulating property of air is lost. Step 4: This breakdown of air allows a sudden flow of charge, which appears as a bright lightning flash. Step 5: Option C correctly describes strong opposite charges breaking down the resistance of the intervening air. Step 6: Therefore, option C is the correct explanation in this context.

Verification / Alternative check:
Scientific descriptions of lightning emphasise charge separation in clouds due to colliding ice particles and other processes. The lower part of a thundercloud may become negatively charged while the upper part becomes positively charged, or a strong charge difference may develop between cloud and ground. Lightning initiates when the electric field intensity exceeds about 3 * 10^6 V/m, causing dielectric breakdown of air. This matches option C's description of strong opposite charges overcoming the resistance of air.

Why Other Options Are Wrong:
Similar charges of electricity rush towards each other and then get repelled: Similar charges repel rather than attract; this does not describe how lightning discharge forms between opposite charges.
Clouds strike against impurities in air and friction burns these impurities: Friction with impurities is not the primary mechanism for lightning, and burning impurities does not capture the role of large-scale electric fields.
Water vapour produces electricity in the clouds: While water and ice play a role in charge separation, water vapour alone does not simply “produce electricity” in the clouds as described here.

Common Pitfalls:
Many learners misuse the idea of “frictional electricity” and think lightning is just friction between clouds and air. Another confusion is believing similar charges can cause lightning by crashing together, which contradicts basic electrostatic principles. To avoid these errors, always connect lightning formation to large potential differences between regions of opposite charge and to the breakdown of air's insulating properties.

Final Answer:
Lightning is produced mainly when strong opposite charges in different regions break down the resistance of the intervening air.