The number of protons in an atom is equal to its: MCQ with Answer and Explanation

The number of protons in an atom is equal to its:
A. Mass number
B. Valency
C. Number of neutrons
D. Atomic number
Answer: Option D
Solution (By JKSSB Mock Tests)
Atomic number (Z) is defined as the number of protons in the nucleus of an atom. It determines the identity of the element. In a neutral atom, the number of electrons equals Z. Mass number = protons + neutrons.

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Practice More chemistry Questions

Question #1
PVC's rigidity in its unplasticized form is due to:
A. Covalent cross-links
B. High molecular weight only
C. Polar C-Cl bonds causing intermolecular attractions
D. Strong hydrogen bonding

Correct Answer: Option C


Explanation:
PVC has polar C-Cl bonds; the chlorine atoms create dipole-dipole interactions between polymer chains, restricting chain movement and making the material rigid and strong. Adding plasticizers (e.g., phthalates) reduces intermolecular forces, making it flexible. Cross-links are in thermosets, PVC is thermoplastic. High molecular weight contributes but polarity is key.

This question belongs to: Science chemistry
Question #2
Which metal is used in the thermal process for welding railway tracks?
A. Zinc
B. Copper
C. Aluminium
D. Iron

Correct Answer: Option C


Explanation:
Thermite reaction: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat. Molten iron produced fills the gap between rails. Aluminium is the reducing agent.

This question belongs to: Science chemistry
Question #3
The reaction of zinc with dilute nitric acid does NOT produce hydrogen because:
A. Zinc does not react with acids
B. Nitric acid is a strong oxidizing agent and oxidizes H₂ to water
C. Zinc is less reactive than hydrogen
D. Nitric acid contains no hydrogen

Correct Answer: Option B


Explanation:
Dilute HNO₃ is an oxidizing agent; it oxidizes the hydrogen produced to water and itself gets reduced to nitrogen oxides (NO, N₂O, etc.). Very dilute HNO₃ with Mg/Mn can produce H₂. Metals above hydrogen normally displace H₂ from non-oxidizing acids like HCl.

This question belongs to: Science chemistry