Out of the musical instruments listed, three are alike in some manner and one is different. Select the odd one.

Violin, Sitar, Guitar→ These are all string instruments played  by plucking or bowing the strings directly.

Piano→ Although it has strings inside, it is a keyboard instrument, and the strings are hit by hammers when keys are pressed.

So, Piano is different because its playing method is keyboard-based, not directly plucking or bowing the strings.

Thus, correct option is (c).