Event A: Indefinite curfew was imposed in Mubarakpur town of U.P. Event B:…

Cause-and-effect reasoning questions test whether you can identify which of two given events triggered the other. The immediate and principal cause is the event that directly, and predominantly, brought the other event about; the effect is the consequence that follows from, and depends on, that cause. The relationship must be judged by real-world causal logic, not by the order in which the events are listed.

Here, Event A is the imposition of a curfew, and Event B is the outbreak of deadly communal clashes. Authorities impose curfews specifically to restore order after violent unrest breaks out; the curfew is a reactive administrative measure. So the clashes (Event B) are what necessitated the curfew (Event A): B is the immediate and principal cause, and A is its effect.

Contrast with the near-miss options:

• 'A is the cause and B is the effect' reverses this dependency; a curfew does not trigger communal clashes, it is imposed to contain them.

• 'A is an effect but B is not the principal cause' correctly treats the curfew as an effect but wrongly denies that the clashes are what drove it, when they are exactly why authorities intervened.

• 'None of these' does not apply, since one of the offered relationships accurately captures how B directly led to A.

Therefore, the correct relationship is that A is the effect and B is its immediate and principal cause.