Question

A monoatomic anion (A⁻) has 45 neutrons and 36 electrons. Atomic mass, group in the periodic table and physical state at room temperature of the element (A) respectively are

• A. 80, 17, liquid
• B. 81, 16, solid
• C. 80, 16, gas
• D. 81, 15, gas

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
By deducing the number of protons from the given electron count of the ion, we can identify the specific element. Once the element is identified, we determine its standard properties (atomic mass, group number, physical state).
Step 2: Key Formula or Approach:
For a monoatomic anion \(\text{A}^-\):
\(\text{Number of electrons} = \text{Atomic Number } (Z) + \text{magnitude of negative charge}\).
\(\text{Atomic Mass } (A) \approx \text{Protons } (Z) + \text{Neutrons}\).
Step 3: Detailed Explanation:
The ion is \(\text{A}^-\), meaning it has gained 1 electron compared to its neutral atomic state.
Given the ion has 36 electrons, the neutral atom \(\text{A}\) must have:
\(\text{Electrons in neutral atom} = 36 - 1 = 35\).
Therefore, the atomic number \(Z = 35\).
The element with atomic number 35 is Bromine (\(\text{Br}\)).
Let's find the required properties for Bromine (\(\text{Br}\)):
1. Atomic mass: Protons + Neutrons = \(35 + 45 = 80\).
2. Group in the periodic table: Bromine is a halogen, which belongs to Group 17.
3. Physical state at room temperature: Bromine is one of the only two elements on the periodic table (along with Mercury) that is a liquid at standard room temperature.
Comparing these findings: 80, 17, liquid.
Step 4: Final Answer:
The properties respectively correspond to option A.