12. the number of protons and neutrons tells us:
| a. the principle quantum
number
b. the reactivity of the element e
c. the atomic mass
d. the atomic number
. both a and c

c. The atomic mass

Explanation:

The atomic mass is the total number of protons and neutrons which are present in the atomic nucleus of an element. All atomic nucleus have protons and neutrons except by exception of common form of hydrogen H+.

Mass number or atomic mass = proton number + neutrons number

each  column  of the  table  is called a group. elements in a group share similar properties. groups are  read  from  top  to  bottom. metal. metalloid. nonmetal. solid. liquid. gas. fe. hg. o.  2. 3. 4. 5. 6. 7. 8. 9.  2. beryllium. 9.012. 4.  sodium. 22.990.  11. 3.  magnesium. 24.305.  12.  potassium. 39.098.  19. 4.  calcium. 40.078.  20. i guess  i  

the ratio of the conjugate base to the acid required to attain the desired ph.