How many sub-atomic particles are contained in 27/13 X3+?

The atomic number (the subscript 13) indicates the number of protons.
Number of protons = 13.

The mass number (the superscript 27) is the sum of protons and neutrons.
Number of neutrons = Mass number - Number of protons = $27 - 13 = 14$.

For a neutral atom, the number of electrons equals the number of protons (13). The charge of the ion is +3, meaning it has lost 3 electrons.
Number of electrons = $13 - 3 = 10$.

Total particles = Protons + Neutrons + Electrons = $13 + 14 + 10 = 37$.

• D. 37

14. Magnesium oxide is an example of
Magnesium oxide ($\text{MgO}$) is formed from a metal (magnesium) and oxygen. Metal oxides typically exhibit basic properties, meaning they react with acids.

• A. a basic oxide.

15. A particle that is made up of 10 electrons and 13 protons is

Net charge = (Number of protons) - (Number of electrons) = $13 - 10 = +3$.

A particle with a net positive charge is called a cation.

• D. a cation.

16. A molecule is the smallest independent particle of
A molecule is defined as the smallest particle of a substance (element or compound) that retains the chemical and physical properties of that substance and is capable of independent existence. While not all elements exist as discrete molecules (e.g., metals or noble gases), many do (e.g., $\text{O}_2$, $\text{N}_2$, $\text{Cl}_2$). Among the given options, "an element" is the most fitting description for substances that can form molecules.

• C. an element.