Circle only those of the following reactions that are redox reactions:
k2cro4 + bacl2 ? bacro4 + 2 kcl
cu+s ? cus
agno3 + hcl ? hno3 + agcl
2 na + 2 h2o ? 2 naoh + h2
mgbr2 + 2 naf ? mgf2 + 2 nabr
2 co + o2 ? 2 co2
so2 + h2o ? h2so3

options B,D and F

Explanation:

Since redox reactions are those which involves both oxidation and reduction

In B , Cu is oxidized and S gets reduced

D, Na gets oxidized and hydrogen gets reduced

F, carbon gets oxidized and Oxygen gets reduced

In g, there is no change in oxidation no of s in both product and Reactants is same +4

Similarly in the case of Ag and Mg.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.