What is the mass number of an atom which contains 21 electrons,21 protons and 24 neutrons

What happened in 2012 and how does it illustrate the importance of understanding the sun and how it works?

How much would the freezing point of water decrease if 4 mol of sugar were added to 1 kg of water(k=1.86 c/mol/kg for water and i=1 for sugar

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation: