Question

An element \( M \) has an atomic mass of 19 and atomic number 9, its ions are represented by:

• A. \( M^+ \)
• B. \( M^{2+} \)
• C. \( M^- \)
• D. \( M^{2-} \)

Hint:

Elements with atomic numbers less than 18 often form negative ions by gaining electrons to achieve a stable electron configuration.

Answer 1

The Correct Option is C

Step 1: Determine the number of electrons in the element.
The atomic number of \( M \) is 9, which means it has 9 protons and 9 electrons in its neutral state. The atomic mass of 19 indicates the number of protons and neutrons combined. For a neutral atom, the number of electrons equals the atomic number.

Step 2: Consider the possible ions.
- \( M^+ \): This would mean the element has lost one electron, making it positively charged. However, since the element has 9 electrons in its neutral state and no information suggests it has lost an electron, this is incorrect.
- \( M^{2+} \): This would imply the element has lost two electrons, which is not typical for this element.
- \( M^- \): This indicates the element has gained one electron, which makes the ion negatively charged. Since the element can gain an electron to become stable, this is the correct answer.
- \( M^{2-} \): This would imply the element has gained two electrons, which is less common for this element.

Step 3: Conclusion.
The correct answer is (3), \( M^- \), because the element would likely gain one electron to form a stable ion.