The bond formed b/w NH3and BF3is co-ordinate covalent bond because NH3 is_ due to presence of one lone pair:

Explanation

Option B is correct.A donor species is a substance that can donate electrons to another substance. This type of bonding is called a coordinate covalent bond. The bond formed between ammonia (NH3) and boron trifluoride (BF3) is a coordinate covalent bond because NH3 is a donor due to the presence of one lone pair of electrons. A coordinate covalent bond is a type of covalent bond in which one atom donates both of the shared electrons. In the case of NH3 and BF3, the nitrogen atom in NH3 donates its lone pair of electrons to the boron atom in BF3. The boron atom in BF3 has a vacant valence orbital, and it is able to accept the lone pair of electrons from the nitrogen atom. The coordinate covalent bond between NH3 and BF3 is shown below: [N ::: H]--> F : B The arrow indicates that the lone pair of electrons from the nitrogen atom is being donated to the boron atom. The coordinate covalent bond between NH3 and BF3 is responsible for the formation of the compound ammonium trifluoride (NH4F). Ammonium trifluoride is a white solid that is soluble in water. It is used as a catalyst in the production of nitrogen-containing compounds. The nitrogen atom in NH3 is a donor because it has a lone pair of electrons that it can donate to another atom. The boron atom in BF3 is an acceptor because it has a vacant valence orbital that can accept the lone pair of electrons from the nitrogen atom.