Often there are some input pins on chips which you don't require. But there is also notion that input pins should not be left floating or unconnected. So what is the solution?

 

What kind of ic (TTL, CMOS, uC) and which one?

 

Depends upon the circuit.

 

Often there are some input pins on chips which you don't require. But there is also notion that input pins should not be left floating or unconnected. So what is the solution?

On microcontrollers I make unused port inputs into an output pin.
Any other pins I connected to ground.

If you leave pins floating they can oscillate and draw a lot of current.

 

Tie each unused input pin to either the positive power supply or to ground. Choose between power and ground such that it will not interfere with the operation of your circuit. For example on a counter chip tie the reset pint so that reset is not active. In the case of spare gates (when the whole gate is unused), it does not matter.