Tha mass of a proton is approximately equal to that of

Step 1: Analyze the question We are asked which particle has a mass approximately equal to that of a proton.

Step 2: Recall the key concept Approximate masses relative to a proton (mass ≈ 1 atomic mass unit, 1.67 × 10⁻²⁷ kg):

| Particle | Approx. relative mass | |---|---| | Proton | 1 u | | Neutron | 1 u (slightly heavier) | | Electron | about 1/1836 u | | β-particle (a fast electron) | about 1/1836 u | | α-particle (helium nucleus: 2 protons + 2 neutrons) | about 4 u |

Step 3: Compare the options

• A. α-particle: about 4 times the mass of a proton, so it is wrong.
• B. β-particle: this is an electron (or positron), which is far lighter, so it is wrong.
• C. Neutron: about 1 u, nearly identical to the proton (1.675 × 10⁻²⁷ kg vs 1.673 × 10⁻²⁷ kg), so it is correct.
• D. Electron: about 1/1836 of the proton's mass, so it is wrong.

Step 4: Answer The mass of a proton is approximately equal to that of a neutron, which is option C.

Exam tip: Remember that protons and neutrons are both called nucleons and each has a mass of about 1 u. Electrons and β-particles are very light, about 1/1840 u. An α-particle is the same as a helium nucleus, with mass number 4.