Identify the correct pair of elements among the following which are liquid at room temperature and standard pressure.
- A.Bromine and fluorine
- B.Mercury and rubidium
- C.Bromine and thallium
- D.Bromine and mercury
Correct answer
Explanation
The correct answer is D, Bromine and mercury. These are the only two elements that are liquid at standard room temperature and pressure: mercury is a metal and bromine is a non-metal.
Mercury melts at about −39 °C and boils at about 357 °C, so it stays liquid over a wide range, which is why it was used in thermometers and barometers. Bromine melts at about −7 °C and boils at about 59 °C; it is a dense, reddish-brown liquid that gives off choking fumes. A few metals, such as caesium (melting point about 28 °C) and gallium (about 30 °C), turn liquid just above ordinary room temperature, but they are solid at the standard 25 °C.
A is wrong because fluorine is a pale yellow gas. B is wrong because rubidium melts at about 39 °C and is a solid at room temperature. C is wrong because thallium is a soft solid metal that melts at about 304 °C.
Exam tip: liquid elements at room temperature, mercury (metal) and bromine (non-metal).
Practice Questions
View allA negative work is done when an applied force F and the corresponding displacement S are
- A.perpendicular to each other.
- B.parallel to each other.
- C.anti-parallel to each other.
- D.equal in magnitude.
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Work is negative when the force acts opposite to the displacement, because the angle between them is then 180°. Work done is W = F S cos θ, where θ is the angle between the force and the displacement.
Read the full explanation →Which one of the following statements about a satellite orbiting around the Earth is correct ?
- A.Satellite is kept in orbit by remote control from ground station.
- B.Satellite is kept in orbit by retro-rocket and solar energy keeps it moving around the Earth.
- C.Satellite requires energy from solar panels and solid fuels for orbiting.
- D.Satellite does not require any energy for orbiting.
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Once a satellite is placed in orbit with the right speed, the Earth's gravity keeps it going round without any engine.
Read the full explanation →Which one of the following is not a conservative force ?
- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Spring force
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Friction is a non-conservative force because the work it does depends on the path taken and the energy it removes is lost as heat.
Read the full explanation →A microphone converts
- A.electrical signals to sound waves
- B.sound waves to electrical signals
- C.microwaves to sound waves
- D.sound waves to microwaves
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A microphone is a transducer that changes the pressure variations of sound into a matching electrical signal. In a common dynamic microphone, sound waves make a thin diaphragm vibrate.
Read the full explanation →When a light ray passes through from air to water with a non-zero angle the ray will be
- A.bending towards the normal
- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
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Light slows down when it enters water from air, so a ray that strikes the surface at an angle bends towards the normal.
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