It is not clear what is meant by 'beta'. Please rephrase it in a new question.
It's pretty obvious this question is about radioactivity and the beta particles produced by that.
In fact beta particles are not the least penetrating. It is the alpha particles
that penetrate least. That's because they interact easily with atomic nuclei.
Atomic nuclei are positively charged, like alpha particles, causing strong repulsion.
The gamma ray because a photon does not have electric charge and is thus does not experience force in a EM field. All the others are charged particles
Beta particles are negatively charged are electrons and have -1 unit charge and 0 mass. They are very dangerous and have high penetrating power.
Alpha being so massive penetrates with less power. Beta lighter yet massive has less penetrating power. But gamma being just a radiation/non-massive photon penetrates with highest power
Gamma rays are more penetrating than alpha and beta particles.
Alpha particles are the least penetrating, and are not able to pass through a single sheet of paper. Beta particles can penetrate through a sheet of paper, but not a piece of aluminum. Gamma rays can travel through both paper and aluminum and it takes dense material like lead to stop them or reduce their number. Gamma rays are high energy electromagnetic rays.
The gamma ray because a photon does not have electric charge and is thus does not experience force in a EM field. All the others are charged particles
Beta particles have a very low penetrating power; an aluminium foil of 3-4 mm is a sufficient shielding.
The most penetrating power is for beta particles compared to those given here.
alpha, beta, gamma
Gamma Beta Alpha
Beta particles are negatively charged are electrons and have -1 unit charge and 0 mass. They are very dangerous and have high penetrating power.
Alpha being so massive penetrates with less power. Beta lighter yet massive has less penetrating power. But gamma being just a radiation/non-massive photon penetrates with highest power
Gamma rays are more penetrating than alpha and beta particles.
Highest penetration: Gamma (y) Second highest: Beta (B)Weakest penetration: Alpha (a)Explanation: The relative penetrating abilities of alpha, beta, and gamma radiation. The heavy, highly charged alpha particles are stopped by a piece of paper (or the skin). The lighter, less highly charged beta particles penetrate paper, but are stopped by a 0.5-cm sheet of lead. Because gamma rays have no charge and no mass, they are the most penetrating, but can be stopped by several centimeters of lead.
Alpha particles are the least penetrating, and are not able to pass through a single sheet of paper. Beta particles can penetrate through a sheet of paper, but not a piece of aluminum. Gamma rays can travel through both paper and aluminum and it takes dense material like lead to stop them or reduce their number. Gamma rays are high energy electromagnetic rays.
Because there are considerable difference between the three, with respect to electric charge, mass, and energy.
A beta particle has an electric charge of -1 because beta particles are both lightweight and fast moving, they have a greater penetrating power than alpha particles.