Balance this equation (step by step please)

Reactions:

Explanation:

In the reaction, the CrO4(Chromate)  is a compound NO3(Nitrate) is a compound as well.

Ignore the number in front of the reaction first, calculate how many K, Cr, O, Pb and N in the equation for both left and right side.

Left side:   K=2, Cr=1, Pb=1, N=2, O=10

Right side: K=1, Cr=1, Pb=1, N=1, O=7

So we need 3 more oxygen, 1 more nitrogen and 1 more potassium on the right.

If we add a 2 in front of KNO3, there will be 2 potassium, 2 Nitrogen and 6 oxygen, which the reaction complete.

Conclusion:

a is the correct answer