An element with 3 protons and 4 neutrons has a valency of 

The valency of an element is the property of an element that determines the number of other atoms to which an atom of the element can combine. The element which has the 3 protons has 2 protons present in its 'S' shell and 1 electron present in its outermost shell. So, it will try to lose/donate 1 electron in its outermost shell in order to achieve stability that means it has 1 valency.