1 What is the approximate mass of a proton? (1) 1 u (3) 1 g (2) 0.0005 u (4) 0.0005 g 1 2 3 4 Half-n-half Clue 2. 2 An electron in a sodium atom gains enough energy to move from the second shell to the third shell. The sodium atom becomes (1) a positive ion (2) ...