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Chemistry · Question 611
Why does ordinary ice float on liquid water?
Its O-H bonds are longer
Ice has a simple cubic lattice
Its intermolecular forces are weak
Its open hydrogen-bonded structure contains more empty space
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Correct answer: D
Its open hydrogen-bonded structure contains more empty space
The open hydrogen-bonded lattice of ice lowers its density below that of liquid water.
Chemistry · Question 612
An acidic buffer is commonly made from:
A strong acid and its salt with a weak base
A weak acid and its salt with a strong base
A strong acid and its salt with a strong base
A weak acid and its salt with a weak base
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Correct answer: B
A weak acid and its salt with a strong base
An acidic buffer contains a weak acid and its conjugate base, often supplied as a salt with a strong base.
Chemistry · Question 613
What is the decomposition of a substance by electric current called?
Thermolysis
Catalysis
Electrolysis
Photolysis
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Correct answer: C
Electrolysis
Electrolysis uses electric current to drive a non-spontaneous chemical decomposition.
Chemistry · Question 614
Which statement about chemical bonding is incorrect?
A covalent bond can form by overlap of half-filled orbitals
An ionic bond involves attraction between oppositely charged ions
Greater s-character generally produces stronger overlap
Bonds between larger atoms are necessarily stronger
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Correct answer: D
Bonds between larger atoms are necessarily stronger
Larger orbitals usually overlap less effectively, so increasing atomic size does not necessarily strengthen a bond.
Physics · Question 615
The product of force and the time for which it acts equals:
Angular momentum
Force
Change in linear momentum
Velocity
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Correct answer: C
Change in linear momentum
Impulse FΔt equals the change in linear momentum.
Physics · Question 616
Two kilowatt-hours is a quantity of:
Electrical energy
Power
Momentum
Torque
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Correct answer: A
Electrical energy
A kilowatt-hour is power multiplied by time and is therefore a unit of energy.
Physics · Question 617
At the midpoint between two equal positive point charges, how do their electric-potential contributions combine?
They add to twice either single contribution
They reduce to half
They remain equal to one contribution
They cancel
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Correct answer: A
They add to twice either single contribution
Electric potential is a scalar; equal positive contributions at the midpoint add.
Physics · Question 618
If a wire's length doubles and its cross-sectional area halves while resistivity stays constant, its resistance becomes:
Twice the original
Four times the original
Half the original
One quarter of the original
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Correct answer: B
Four times the original
Since R = ρL/A, doubling L and halving A multiplies R by four.
Physics · Question 619
Conversion of alternating current into direct current is called:
Amplification
Rectification
Oscillation
Resonance
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Correct answer: B
Rectification
A rectifier converts alternating current to unidirectional current.
English · Question 620
Choose the grammatically correct sentence.
The Three Musketeers was written by Dumas.
The Three Musketeers were written by Dumas.
The Three Musketeers has written by Dumas.
The Three Musketeers have written by Dumas.
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Correct answer: A
The Three Musketeers was written by Dumas.
A title is treated as a singular work, so it takes 'was written'.