Statement I (True): El Niño = abnormal warming of central/eastern equatorial Pacific → disrupts Walker circulation → weakens Indian summer monsoon → tends to cause drier monsoon in South Asia.
Statement II (True): Tsunami waves have small amplitude and long wavelength in deep ocean (often unnoticed) but shoal and grow in height in shallow coastal waters, becoming destructive.
Tsunami behaviour has nothing to do with El Niño’s impact on the South Asian monsoon. Hence II doesn’t explain I. Therefore, Correct Answer is Option A.