The graph between the strength of the magnet(number of paper clips picked) and battery is approximately a straight line.
For 25 coil, with increase of 1.5 V battery voltage, the electromagnet picks about 5 more clips. So, for a 7.5 V battery, it would pick about 30 paper clips.
For 50 coil, with increase of 1.5 V battery voltage, the electromagnet picks about 15 more clips. So, for a 7.5 V battery, it would pick about 30 paper clips.
This should help
there always needs to be 2 electrons in the first shell then 8 electrons in each shell and continue till you not have any more number of electron left
Normal force is mass x gravity, so mass x 9.81