How many atoms are in 187 g of calcium?

The important relationship or constant we have to know here is the Avogadro's number. 6.022*10^23 /mole. To answer this, we have to convert the mass of Calcium to moles by dividing it with its molar mass. The molar mass of Calcium is 40 g/mol. 



Then we multiply the moles calcium with the Avogadro's constant. 

4.675 moles Calcium * 6.022*10^23 /mole = 2.82*10^24 atoms of calcium. 

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.

Anions are negative charged ions