Question

The mass number of an atom is 15 and its atomic number is 7. Now, this atom absorbs an \( \alpha \)-particle and emits a proton. What will be the mass number of changed atom?

• A. 16
• B. 18
• C. 17
• D. 15

Hint:

Track mass number carefully: \(+4\) for \(\alpha\)-particle, \(-1\) for \(\beta^-\)-particle.

Answer 1

The Correct Option is B

Concept:
• \( \alpha \)-particle: adds mass number 4
• Proton emission: reduces mass number by 1

Step 1: Initial mass number.
\[ A = 15 \]

Step 2: After absorbing \( \alpha \)-particle.
\[ 15 + 4 = 19 \]

Step 3: After emitting proton.
\[ 19 - 1 = 18 \]