Which of the following radiations emitted in radioactive decay has momentum, a fairly high penetrating power and is deflected by a magnet?

Step 1: Analyze the question We need a radiation from radioactive decay that has all three properties:

1. It has momentum (it is a particle with mass and velocity).
2. It has fairly high penetrating power.
3. It is deflected by a magnetic field (it is charged).

Step 2: Review the radiations

| Radiation | Nature | Charge | Penetrating power | Deflected by magnet? | |---|---|---|---|---| | Alpha (α) | Helium nucleus | +2 | Low (stopped by paper) | Yes (slightly) | | Beta (β) | Fast electron | −1 | Moderate/fairly high (passes through paper, stopped by a few mm of aluminium) | Yes (strongly) | | Gamma (γ) | EM wave | 0 | Very high | No | | X-rays | EM wave | 0 | High | No |

Step 3: Eliminate options

• C and D (gamma and X-rays): These are electromagnetic waves with no charge, so a magnet does not deflect them. Eliminated.
• A (alpha): It is charged and has momentum, but its penetrating power is very low, since a sheet of paper or a few centimetres of air stops it. It is not "fairly high". Eliminated.
• B (beta): It is a particle with mass, so it has momentum. It is charged, so a magnet deflects it. Its penetrating power is fairly high, greater than alpha's but less than gamma's. This fits all three properties.

Answer: B (beta particle)

Tip: Remember the order of penetrating power as α < β < γ. For deflection, ask whether the radiation is charged. Alpha and beta are deflected, but gamma and X-rays are not. When a question says "fairly high" or "moderate" penetration together with deflection, think beta.