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:
A monoatomic anion $A^-$ is formed when a neutral atom gains one electron. Therefore, the number of protons in the neutral atom (Atomic Number, $Z$) is one less than the number of electrons in the anion. Atomic mass ($A$) is the sum of protons and neutrons.

Step 2: Key Formula or Approach:
1. Atomic Number ($Z$) = (Electrons in $A^-$) - 1. 2. Atomic Mass ($A$) = $Z$ + Neutrons. 3. Use $Z$ to identify the element and its group.

Step 3: Detailed Explanation:
1. Find Protons: $Z = 36 - 1 = 35$. The element with $Z=35$ is Bromine (Br). 2. Find Atomic Mass: $A = 35 + 45 = 80$. 3. Periodic Table Position: Bromine belongs to Group 17 (Halogens). 4. Physical State: Bromine is the only non-metal that is a liquid at room temperature.

Step 4: Final Answer:
The values are 80, 17, and liquid.