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MCQ Practice

General Science (Everyday Science) MCQs

In SN1 reactions, the rate-determining step is:

  • A. Nucleophilic attack
  • B. Carbocation formation
  • C. Proton transfer
  • D. Solvent evaporation
Explanation:
SN1 rate depends on unimolecular leaving-group departure to form a carbocation.

The major product of complete combustion of an alcohol in excess oxygen is:

  • A. Alkene and water
  • B. Carbon monoxide only
  • C. Carbon dioxide and water
  • D. Aldehyde and hydrogen
Explanation:
Complete oxidation of carbon and hydrogen yields (CO_2) and (H_2O).

Which reagent most directly distinguishes aldehydes from ketones under mild conditions?

  • A. Bromine water
  • B. Tollens’ reagent
  • C. Dilute HCl
  • D. Sodium chloride
Explanation:
Aldehydes reduce Tollens’ reagent whereas ordinary ketones generally do not.

Which species is paramagnetic?

  • A. (Zn^{2+})
  • B. (Sc^{3+})
  • C. (Cu^+)
  • D. (Fe^{3+})
Explanation:
(Fe^{3+}) has five unpaired d electrons, making it strongly paramagnetic.

The standard cell potential for a spontaneous galvanic cell is:

  • A. Negative
  • B. Zero
  • C. Positive
  • D. Infinite
Explanation:
A spontaneous cell has (E^\circ_{\text{cell}} > 0).

In electrochemistry, the anode is the electrode where:

  • A. Reduction occurs
  • B. Oxidation occurs
  • C. Electrons enter the cell from external circuit
  • D. Cations are always reduced
Explanation:
Oxidation always occurs at the anode by definition.

Which statement about electron affinity is generally correct?

  • A. It becomes less exothermic across a period
  • B. Noble gases usually have strongly negative values
  • C. Halogens tend to have highly exothermic electron affinities
  • D. It is identical to ionization energy
Explanation:
Halogens readily gain one electron to complete their valence shell.

For an ideal gas undergoing adiabatic free expansion into vacuum, the temperature change is:

  • A. Always increases
  • B. Always decreases
  • C. Remains unchanged
  • D. Depends only on volume ratio, not gas type
Explanation:
For an ideal gas, internal energy depends only on temperature and does not change in free expansion.

Which process is always endothermic?

  • A. Condensation
  • B. Freezing
  • C. Sublimation
  • D. Deposition
Explanation:
Sublimation requires energy to overcome intermolecular forces from solid to gas.

The common-ion effect suppresses the ionization of a weak acid because it:

  • A. Increases (K_a)
  • B. Shifts equilibrium toward undissociated acid
  • C. Eliminates water autoionization
  • D. Makes the acid strong
Explanation:
Added common ion drives dissociation equilibrium to the left.