Question

question 17 (1 point)
(02.02 mc)
the image shows the representation of an unknown element in the periodic table.
based on the representation, which of the following statements about the element is true?
a the number of neutrons in an atom of the element is 24.
b the combined mass of all the protons and electrons is 24.305.
c the combined mass of all the neutrons and electrons is 24.305.
d the mass number of the most common isotope of the element is 24.

Explanation:

Step1: Identify atomic number and atomic mass

The atomic number is 12, and the atomic - mass is 24.305. The atomic number (Z) is the number of protons. For a neutral atom, the number of electrons is equal to the number of protons.

Step2: Recall mass - number and neutron number relationships

The mass number (A) is the sum of protons and neutrons. The atomic mass is the weighted average of the masses of all naturally - occurring isotopes of the element. The most common isotope of an element with atomic number 12 (magnesium) has a mass number close to the rounded - off atomic mass. Rounding 24.305 gives 24.

Step3: Analyze each option

• Option a: The number of neutrons \(n=A - Z\). For \(Z = 12\) and \(A\approx24\), \(n = 24-12=12\), not 24.
• Option b: Electrons have very little mass compared to protons and neutrons. The combined mass of protons and electrons is not equal to the atomic mass which is mainly due to protons and neutrons.
• Option c: Similarly, electrons have negligible mass compared to neutrons and protons, so the combined mass of neutrons and electrons is not equal to the atomic mass.
• Option d: The most common isotope of magnesium has a mass number of 24. This is consistent with the rounded - off value of the atomic mass.

Answer:

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