You have a comparator circuit, the chip compares the two inputs.

If the +ve input is +ve with respect to the -ve input, there will be an output.

If the -ve input goes more +ve than the +ve input, the output will be switched off.

Therefore -ve input has to be more +ve than +ve input, compared to ground, or negative of Battery.

http://en.m.wikipedia.org/wiki/Comparato...

This should explain everything.

The voltage should be greater than 5 volts

Anything less than 5V

>insert vaguely sciencey answer here<

A. > + 5V.

Just doing a quiz online and have no idea about this question? Any input at all is much appreciated! Thanks for your help.