It is possible for a particular element to have various number of neutrons

What is the volume of 2.5 moles of nitrogen gas (n2)at standard temperature and pressure (stp)?

110 g of water (specific heat = 4.184 j/g c) and 100 g of a metal sample (specific heat = 0.397 j/g c) are heated from 25 degrees c to 75 degrees c. which substance required more thermal energy?

If you try to move a piano and are unable to move it, did you perform any work in the scientific sense of the word? yes or no?