A key of mechanical piano is first struck gently and then struck again but much harder this time. In the second case:
(a) sound will be louder but pitch will not be different
(b) sound will be louder and the pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected

 If a key of mechanical piano is first struck gently and then struck again but much harder this time. In the  second case sound will be louder but pitch will not be different.

So, option (a) is correct.