Ca + 2HCl = CaCl₂ + H₂
c=4.50 mol/l
v=2.20 l
n(HCl)=cv
m(Ca)/M(Ca)=n(HCl)/2
m(Ca)=M(Ca)cv/2
m(Ca)=40g/mol·4.50mol/l·2.20l/2=198 g
198 grams of Ca are needed
Phosphorus has 16 neutrons. Phosphorous is 15 on the periodic table, which means that the atomic number (number of protons) of phosphorous is 15.
For more info: https://study.com/academy/answer/what-is-the-number-of-neutrons-in-phosphorus.html
Ca, V, Cu, Kr
Remember a period is a the horizontal rows in the Periodic Table.