Question

how does boron have - 3 valency, I understood abt +3 as it loses 3 electrons, some1 explain the reason for - 3 properly, srsly Indians can only mug things up No1 can answer these logical questions ​

Answer 1

Boron atom can only lose electrons to gain stability by attaining the electronic configuration of the nearest Nobel gas, here it is Helium. Boron can not gain electrons!  

when an atom gains electrons it acquires a negative charge. This is so because electrons are negatively charged.

Here atom gains 3 electrons to attain the electronic configuration of the nearest noble gas to gain stability.

Answer 2

Boron loses electron, so as to gain stability. It is of positive valency, hence it cannot gain electrons- which would make it negatively charged.