Which nitrogen trihalide is least basic?

Hint : We know that the basicity of the substance increases as the number of +I (inductive effect) groups increases while the basicity decreases as the number of \[\left( -I \right)\] groups increases. Before that we must know that the Inductive effect is an effect on the transmission of unequal bonding electron sharing through a chain of atoms in a molecule, resulting in a permanent dipole in a bond.

Complete Step By Step Answer:
In the previous classes of chemistry, we have studied in detail about how to write the reactions with the given data and also about balancing the given chemical equation. A chemical equation is the interpretation of the substances which reacts together to form a new or modified substance. The compounds which react with each other are called reactants and the compounds which are newly formed are called as the products.
The reactants that are written on the left hand side of the reaction and products on the right hand side of the equation which is separated by an arrow that represents the reaction going from hand right to left hand side.
The basicity increases down the group because the electronegativity decreases down the group. Base need to be able to donate electrons. Fluorine being the most electronegative draws the electron density towards it and thus it is difficult for nitrogen atom to donate the lone pair of electron. Down the group as electronegativity decreases the basicity increases. Thus, $N{{F}_{3}}$ is least basic nitrogen trihalide.

Note :
Remember that balancing of this chemical equation is nothing but making the number of moles of each atom on the reactant side to be equal to that of the product side. We shall now see how to write the above given data in the form of a chemical equation and balancing it.