A non-metallic element of group 13, used in making bullet prrof vests is extremely hard solid of black colour. It can exist in many allotroic forms and has unusally high melting point. Its trifluoride acts as Lewis acid towards ammonia. The element exhibits maximum covalency of four. Identify the element and write the reaction of tits triffuoride with ammonia. Explain why does the trifuoride act as Lewis acid.

Explanation

The available information suggests that the element is boron, Boron trifulouride reacts with ammonia to form an addition product.

for the lewis acid character of `BF_3` consult section 11.2