Third quarter (or last quarter)
B3+ is isoelectronic with helium.
Isoelectronicity is the phenomenon whereby two or more molecular entities have the same number of electrons or similar electronic configuration regardless of the nature of the elements that are involved.
In the question given above, helium and B3+ have the same number of electrons. Helium has two electrons. Boron has five electrons but it has given away three of the electrons [that is why it has a charge of +3] and it now has only two left.
This is an acid-base reaction where HF is the acid and H2O is the base (it's amphoteric and can be an acid or a base). The products would then H3O+ (the conjugate acid) and F- (the conjugate base). Now, we can simply construct a reaction using the found products and reactants. This acid-base reaction would be HF + H2O <--> H3O+ + F-.
Hope this helps!
#1. The condition of the atmosphere at a certain time and certain place
#2. The rate of evaporation is EQUAL to the rate of condensation
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