What is the overall charge of an atom with 18 protons, 18 neutrons, and 19 electrons?

as no. of protons is equals to the no. of electrons so, it is a neutral atom.

but, as Atomic No. = Mass No. - No. of neutrons

Atomic No. = No. of protons = 18

so, Mass No. = Atomic No. + No. of Neutrons= 18 + 20 = 38

so, correct option is C.

Explanation:

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6