Question 32

An atom after a proton is emitted from its nucleus has A-1, Z-1.

When a proton is emitted from the nucleus of an atom, the atomic mass decreases by 1 and the atomic number also decreases by 1, leading to the values A-1 and Z-1.

A) A+1, Z-1

This option is incorrect because if a proton were to be added to the nucleus, the atomic mass would increase by 1 (A+1), while the atomic number would increase by 1 (Z+1). However, since a proton is emitted, neither condition applies here.

B) A-1, Z+1

This choice is incorrect as it suggests that the atomic mass decreases by 1 (which is correct) but incorrectly states that the atomic number increases by 1. Emission of a proton results in a decrease in the atomic number.

C) A+1, Z+1

This option is incorrect because it implies that both the atomic mass and atomic number increase. Since a proton is emitted, the atomic mass should decrease by 1 and the atomic number should also decrease by 1, making this option invalid.

D) A-1, Z-1

This is the correct answer. When a proton is emitted, the atomic mass (A) decreases by 1 and the atomic number (Z) also decreases by 1, accurately reflecting the changes in the atom's structure.

Conclusion

The correct answer, A-1 and Z-1, clearly describes the changes that occur when a proton is emitted from an atom's nucleus. Options A, B, and C misrepresent the effects of proton emission, failing to accurately reflect the decrease in both atomic mass and atomic number. Thus, D stands out as the only valid option.