The image shows the representation of an unknown element in the periodic table. a square is shown. inside the square twelve is written at the top righthand side. to the middle left side, symbol is written. below it name is written. and further below near the bottom edge of the square, twenty-four point three zero five is written. based on the representation, which of the following statements about the element is true?
the number of neutrons in an atom of the element is 24.
the combined mass of all the protons and electrons is 24.305.
the combined mass of all the neutrons and electrons is 24.305.
the mass number of the most common isotope of the element is 24.

The correct answer is the mass number of the most common isotope of the element is 24.

Explanation:

We are given:

An element having atomic number 12 is magnesium and atomic mass of the element is 24.305

The image corresponding will be

The number '24.305' is the average atomic mass of magnesium element.

Average atomic mass is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

Average atomic mass of magnesium = 24.305 amu

As, the average atomic mass of magnesium lies closer to the mass of Mg-24 isotope. This means that the relative abundance of this isotope is the highest of all the other isotopes.

The 'Mg-24' isotope is the most common isotope of the given element.

Hence, the correct answer is the mass number of the most common isotope of the element is 24.