Which one of the following metals does not react with oxygen directly?
- A.Ti
- B.Fe
- C.Pt
- D.Zn
Correct answer
Explanation
The correct answer is C, Pt. Platinum is a noble metal and does not combine with oxygen even when heated in air.
Metals low in the reactivity series, such as gold and platinum, hold on to their electrons very firmly, so oxygen cannot pull them away under ordinary conditions. That is why platinum stays bright for centuries and is used in jewellery, laboratory crucibles, electrodes and the catalytic converters of cars. Its resistance to corrosion is the very reason it is called a noble metal.
A is wrong: titanium reacts with oxygen at once and forms a thin, tough oxide film, which in fact protects it from further corrosion.
B is wrong: iron combines with oxygen, slowly as rust in moist air and quickly when heated, forming iron oxides.
D is wrong: zinc burns in air on strong heating to give white zinc oxide and forms an oxide layer even at room temperature.
Exam tip: gold and platinum do not react with oxygen; that is why they are called noble metals.
Practice Questions
View allThe speed of the wind is measured by
- A.wind vane
- B.wind rose
- C.barometer
- D.anemometer
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An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.
Read the full explanation →Brilliance of diamond is due to
- A.interference of light
- B.diffraction of light
- C.polarization of light
- D.total internal reflection of light
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Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.
Read the full explanation →Which one of the following is NOT an electromagnetic wave ?
- A.Light wave
- B.Radio wave
- C.Sound wave
- D.Micro wave
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Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves. Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum.
Read the full explanation →Which one of the following is NOT true for an electromagnetic wave ?
- A.Electromagnetic wave transports energy and momentum
- B.Electromagnetic wave can be polarized and reflected
- C.Electromagnetic wave is longitudinal
- D.Electromagnetic wave propagation is described by the varying electric and magnetic fields
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Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.
Read the full explanation →Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
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The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
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