Which reaction is endothermic?
ohci + naoh - nacl + h2o + 58 kj
| 6co2 + 12h20 + energy -> cgh12o6 + 602 + 6h20
2na + cl2 → 2nacl + energy
2c2h6 + 702 -> 4co2 + 6h20 + 2,502 kj

6CO2+12H2O+energy = C6H12O6+6O2+6H2O this reaction is an endothermic reaction.

Explanation:

Endothermic reaction is a specific type of reaction that consume energy in form of heat.In simple words the chemical or biochemical reaction that requires energy from outside is called endothermic reaction.

     6CO2+12H2O+energy  =  C6H12O6+6O2+6H2O

This the only reaction among the 4 reactions mentioned in the question, requires energy.From that point of view it can be stated that the above reaction is an endothermic reaction.

your answer would be a. 12.5 kg

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."