The octet rule tells us that for an atom to be stable it must have 8 electrons in its last energy level. These electrons are called valence electrons. We must see in each compound how the electrons and bonds are distributed. Let's take into account the valence electrons of each element.
These valence electrons coincide with the group to which they belong, that is, if you belong to group 1 they will have 1 valence electron, if they belong to group 7 they will have 7 valence electrons.
We will also make some Lewis diagrams to have greater clarity of how many electrons each element will have. The one that has less than 8, without taking into account the hydrogen will be the option to choose.
The valence electrons of each element is:
H: 2
O: 6
B: 3
N: 5
The Lewis diagrams of each compound will be:
In the image, we see the diagrams of each compound. The purple dots correspond to hydrogen electrons and the yellow ones to the electrons of the other compounds, the electrons are shared. f we count the electrons of the compounds other than hydrogen, we will see that BH3 does not meet the eight electrons
So, the answer will be B) BH3