Which chemical equation is balanced to show that mass is conserved during the reaction?

A Na + Cl2 -> NaCl

B 2H2 O2 -> 2H2 O + O2

C Ch4 + O2 -> Co2 + 2H2 O

D AgNo3 + MgCl2 -> AgCl + MgNO3

A

B

C

D

All of the given chemical equations are balanced, which means that they show that mass is conserved during the reaction.