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Chemistry · Question 461
Why could Rutherford’s classical atomic model not explain a stable atom?
It assumed no empty space in the atom
It contained no nucleus
It contained no electrons
An accelerating orbiting electron should radiate energy and spiral into the nucleus
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Correct answer: D
An accelerating orbiting electron should radiate energy and spiral into the nucleus
Classical electrodynamics predicts that an orbiting charged electron loses energy, so Rutherford’s model could not explain atomic stability.
Chemistry · Question 462
Which statement about first ionisation energies is correct?
Calcium has a higher value than beryllium
Calcium has a lower value than strontium
Calcium has a lower value than magnesium
Calcium has a lower value than barium
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Correct answer: C
Calcium has a lower value than magnesium
First ionisation energy generally decreases down Group 2: Be > Mg > Ca > Sr > Ba.
Chemistry · Question 463
For 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH = −188.3 kJ mol⁻¹. What happens to the equilibrium constant when temperature rises?
It decreases
It increases because of pressure
It remains unchanged at every temperature
It is increased by a catalyst
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Correct answer: A
It decreases
Heating favours the endothermic reverse direction, so the equilibrium constant for the forward exothermic reaction decreases.
Chemistry · Question 464
Bleaching powder is produced by passing chlorine over:
Calcium carbonate
Anhydrous calcium sulphate
Hydrated calcium sulphate
Calcium hydroxide
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Correct answer: D
Calcium hydroxide
Chlorine reacts with dry slaked lime, Ca(OH)₂, to produce bleaching powder.
Chemistry · Question 465
Which halogen is found naturally in compounds where it has a positive oxidation state?
Chlorine
Bromine
Fluorine
Iodine
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Correct answer: D
Iodine
Iodine occurs in oxyanions such as iodate, where iodine has a positive oxidation state.
Chemistry · Question 466
Neoprene synthetic rubber is produced by polymerising:
Acetylene
Divinyl acetylene
Chloroprene
Chloroform
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Correct answer: C
Chloroprene
Neoprene is polychloroprene, formed by addition polymerisation of chloroprene.
Chemistry · Question 467
Which functional group characterises a carboxylic acid?
Carboxyl group
Hydroxyl group only
Aldehyde group
Amino group
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Correct answer: A
Carboxyl group
Carboxylic acids contain the carboxyl functional group, −COOH.
Biology · Question 468
Active transport across a cell membrane is driven directly by:
Simple diffusion
Concentration gradients alone
ATP-powered pumps
Phagocytosis only
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Correct answer: C
ATP-powered pumps
Active transport uses membrane proteins powered by ATP to move substances against gradients.
Biology · Question 469
A stack of cisternae together with associated vesicles forms the:
Golgi apparatus
Ribosome
Lysosome
Peroxisome
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Correct answer: A
Golgi apparatus
The Golgi apparatus consists of flattened membrane-bound cisternae and associated vesicles.
Biology · Question 470
Which structure can function as a secondary lysosome?
Contractile vacuole
Digestive vacuole
Nucleus
Central plant vacuole only
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Correct answer: B
Digestive vacuole
A secondary lysosome forms when a primary lysosome fuses with a vesicle containing material to digest.