Alpha particles pose health risk primarily when they are:

Alpha particles pose health risk primarily when they are:

• A. Completely harmless outside the body.
• B. Able to travel long distances through air.
• C. Positively charged particles that are relatively slow moving and weak; can cause problems when inhaled or ingested.
• D. Blocked completely by a sheet of paper.

Answer: (C)

Alpha particles are heavy, positively charged particles that ionize strongly but have very limited penetrating ability. Because of this, they pose little external hazard—their energy is mostly stopped by a sheet of paper or by a few centimeters of air and they cannot penetrate the skin. The real health risk comes when these particles are inside the body, such as after inhalation or ingestion, where they deposit energy directly in tissues and organs, causing significant ionization and cellular damage. That internal exposure is why they are dangerous despite their weak external penetration.

Alpha particles are heavy, positively charged particles that ionize strongly but have very limited penetrating ability. Because of this, they pose little external hazard—their energy is mostly stopped by a sheet of paper or by a few centimeters of air and they cannot penetrate the skin. The real health risk comes when these particles are inside the body, such as after inhalation or ingestion, where they deposit energy directly in tissues and organs, causing significant ionization and cellular damage. That internal exposure is why they are dangerous despite their weak external penetration.