Option 1 is a voltmeter, it is used to measure the potential difference, or voltage, between two points in an electric circuit - so it doesn`t convert mechanical energy into electrical energy.

Option 2 is an ammeter, which is an instrument for measuring electric current in amperes. Again, it is not a device for energy conversion.

Option 3 is a motor. A motor converts electrical energy to mechanical energy, essentially doing the reverse of what the question is asking.

Option 4 is a generator. A generator is the correct answer because it actually does convert mechanical energy into electrical energy. When the generator`s shaft is rotated mechanically, for example by wind power, steam power, water power, etc., it produces a flow of electric charge (current) via electromagnetic induction. That is why this is the correct answer.