Question

How many protons,neutrons and electrons are present in an atom of hafnium,hf,with a mass number of 178?

Answer 1

178 of each species
178 protons
178 neutrons
And 178 electrons

Answer 2

Answer:

72 protons

102 neutrons

72 electrons

Explanation:

Hf has an atomic number of 72. By definition, this means that it has 72 protons.

It also has a mass number of 178. The mass number (A) counts all elements with significant mass (protons and neutrons). Then,

A = p⁺ + n⁰

n⁰ = A - p⁺ = 178 - 72 = 102

Hf has 102 neutrons.

Elemental Hafnium is electrically neutral because it has the same amount of  positive charges (protons) and negative charges (electrons). Then, it must have 72 electrons.