Într-un amestec de „x” molecule de hidroxid de amoniu NH4OH și 7 molecule de apă se găsesc 39 atomi de hidrogen. Valoarea lui „x” este
3
4
5

\large \boxed{5}  

Explanation:

Molecules of NH₄OH do not exist.

If they did, however, here is how you might answer.

     Total H atoms = 39 H

                   -7H₂O = 14    

H atoms available = 25 H

Each "molecule" of NH₄OH contains five H atoms.

- decrease the number of plants and animals living in the water.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.