How can a student use a diagram to calculate the atomic mass for the helium atom

thats a little if u want the answer just look it up on google thats what i do haha : )

the number of protons in the nucleus of a given element. has slight luster and conducts electricity at high temperatures like metal.but like a nonmetal,boron is brittle and does not conduct electricity well at low temperatures. in graphite, carbon is a soft,brittle solid.it is reflective,ductile,or malleable.

i do not get it   at all

the answer is c. nacl