Which element must be present in an organic compound? (1) hydrogen (3) carbon(2) oxygen (4) nitrogen

the answer is 3) carbon

main component of organic compounds are the element carbon

C forms covalent compounds with other C atoms and form long chains resulting in forming compounds that are very useful to us in our day to day life

human body is made of 4 types of organic molecules.

C covalently bonds with other atoms such as H, O and N etc. forming a large array of useful compounds

1 a

2 d

3 a

4 c

explanation:

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.