Particles Emitted in Radioactive Decay Have Different Penetrating Power $\alpha$ Particle
B) A Radioactive

Particles emitted in radioactive decay have different penetrating power. The penetration depths of two particles, labeled X and Y, in a column of water are shown below. The X particle most likely is ________

A) an $\alpha$ particle.
B) a $\beta$ particle.
C) a positron.
D) a $\gamma$ ray.