Deflection depends on charge sign and mass in electric fields

Steps:

• β-particle (electron) has negative charge and low mass, so it deflects strongly opposite to the field direction.
• α-particle has positive charge (+2e) and high mass (≈7300 times electron mass), so it deflects weakly in the field direction.
• At same initial speed, path is parabolic; deflection magnitude scales with q/m ratio.
• α-particle's q/m is much smaller than β-particle's, resulting in minimal opposite deflection.

Why B is correct:

• B shows slight deflection opposite to β-particle's path, matching α-particle's positive charge and low q/m ratio per F = qE and a = F/m.

Why the others are wrong:

• A: Wrong direction; α-particle deflects with field, not against.
• C: Excessive deflection; α-particle's high mass causes minimal curve.
• D: No deflection; charged α-particle must curve in electric field.

Final answer: B