What is the total number of neutrons in the nucleus of a neutral atom that has 19 electrons and a mass number of 39

NO OF NEUTRON =MASS NO -ATOMIC NO

=39-19

=20

bcz atomic no is equal to no of electrons

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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.