The Sri Lanka Broadcasting Corporation broadcasts its programmes on the 25 metre band. This band is a part of the high frequency (HF) range, which typically spans from 3 MHz to 30 MHz. Option 1, 16 KHz, is incorrect as it falls in the kilohertz (kHz) range, which is lower in frequency compared to the Megahertz (MHz) range. Option 2, 2.2 KHz, is also incorrect for the same reason.

Option 3, 90 MHz, is not the correct answer because it is in the very high frequency (VHF) range, which is typically used for FM radio and television broadcasting. The 25 metre band falls within the HF range, not VHF.

The correct answer is option 4, 12 MHz. This falls within the HF range and is a frequency commonly used for shortwave broadcasting. Shortwave radio signals in the HF range can travel long distances due to their ability to bounce off the ionosphere, making them suitable for international broadcasting.