Four instruments have been given, out of which three are alike in some manner and one is different. Select the one that is different from the rest:

Analysis of each instrument:

Udometer: An instrument used to measure rainfall. The term derives from Latin "udus" meaning wet or moist.

Deciblemeter: An instrument used to measure sound intensity or loudness, expressed in decibels.

Ombrometer: An instrument used to measure rainfall. The term derives from Greek "ombros" meaning rain.

Pluviometer: An instrument used to measure rainfall. The term derives from Latin "pluvius" meaning rain.

Three instruments (Udometer, Ombrometer, and Pluviometer) measure the same physical quantity: rainfall.

One instrument (Deciblemeter) measures a completely different physical quantity: sound intensity.

Therefore, the Deciblemeter is different from the rest.

The correct answer is Option 2: Deciblemeter.