2. J.J. Thomson discovered the negatively-charged particle of atom called ________.
A. orbital C. block
B. nucleus D. particle
3. The element Silicon has three isotopes: Si-28, Si-29, Si-30. If the atomic number of Silicon is 14, how many neutrons does its three isotopes have respectively?
A. 14, 14, 14 C. 14, 17, 13
B. 14, 18, 22 D. 14, 15, 16