The compound calcium cyanamide (cancn) is used as a nitrogen source for crops. to obtain this compound, calcium carbide is reacted with nitrogen at high temperatures. cac2(s) + n2(g) cancn(s) + c(s) what mass of cancn can be produced if 7.45 mol cac2 reacts with 5.85 mol n2?

N2 + CaC2 = CaNCN + C 
As you can see, 1 mol of N2 can react completely with 1 mol of CaC2 and 1 mol of CaNCN will be obtained 
It means 5 mol of N2 can react completely with 5 mol of CaC2 and 5 mol of CaNCN will be obtained 

So, there are 7.5 - 5 = 2.5 odd mole of CaC2 after the reaction 
And the mass of obtained CaNCN is 
m = n*M = 5*80 = 400g

The se-ci  bonds is more polar  than s-br bond

Ithink that one is (c)