12. Which of the following species has the least mass?
A. Electron C. Hydrogen ion
B. Helium atom D. Neutron
13. The mass number of an element whose
atom contains 13 electrons, 13 protons and
14 neutrons is
A. 13 B. 26 C. 27 D. 40
14. Which of the following elements exhibits
variable oxidation states and forms

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

In which of these cases are the two wave points considered to be in phase with each other?

What rule is used to determine how many covalent bonds an element can form? a. the number of covalent bonds is equal to six c the number of covalent bonds is equal to five minus the group number plus the group number b. the number of covalent bonds is equal to eight d. none of the above minus the group number select the best answer from the choices provided