Which one of the following is considered as a compound ?
- A.Silicon
- B.Tin
- C.Sugar solution
- D.Calcium carbonate
Correct answer
Explanation
The correct answer is D, Calcium carbonate. Calcium carbonate, CaCO3, is a compound because calcium, carbon and oxygen are chemically combined in it in a fixed ratio. It occurs in nature as limestone, chalk and marble, and it makes up eggshells, sea shells, pearls and coral. On strong heating it breaks down into quicklime (calcium oxide) and carbon dioxide, a reaction used in making cement and lime, and the change can be undone only by chemical means, which shows it is a compound and not a mixture. Option A is wrong because silicon is an element, a metalloid with symbol Si, widely used in computer chips and solar cells. Option B is wrong because tin is also an element, a metal with symbol Sn, used in solder and for coating iron in tin cans. Option C is wrong because sugar solution is a homogeneous mixture of sugar and water; its composition can vary, and the sugar can be recovered by simple evaporation. Exam tip: CaCO3 = limestone, chalk, marble; heating gives CaO (quicklime) + CO2; adding water to quicklime gives slaked lime, Ca(OH)2.
Practice Questions
View allChlorophyll in photosynthetic prokaryotic bacteria is associated with
- A.plastids
- B.membranous vesicles
- C.nucleoids
- D.chromosomes
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Photosynthetic bacteria have no chloroplasts; their pigments sit on infoldings of the cell membrane that form vesicles or sacs, often called chromatophores.
Read the full explanation →Fat in human body is stored in
- A.Adipose tissue
- B.Red blood cells
- C.Muscle tissue
- D.Epithelial tissue
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Adipose tissue is a loose connective tissue whose cells, called adipocytes, are built to store fat. Each cell holds a large droplet of fat that pushes the nucleus and cytoplasm to one side.
Read the full explanation →Which one of the following is a metalloid ?
- A.Germanium
- B.Coke
- C.Iodine
- D.Sugar
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Germanium is a metalloid, an element whose properties lie between those of metals and non-metals. It is a hard, shiny, grey-white solid like a metal, yet it is brittle and conducts electricity far less well than a metal, which makes it a semiconductor.
Read the full explanation →A photon of X-ray has energy of 1 keV. A photon of visible radiation has energy of 3 eV. In this context, which one of the following statements is not correct?
- A.The wavelength of X-ray photon is less than the wavelength of visible radiation photon.
- B.Both the photons have different energies.
- C.The speeds of both the photons in vacuum are different.
- D.The frequency of X-ray photon is higher than the frequency of visible radiation photon.
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This statement is wrong because every photon, whatever its energy, travels in vacuum at the same speed of light, about 3 × 10^8 metres per second.
Read the full explanation →Which of the following substances cause temporary hardness in water?
1. Mg(HCO3)2
2. Ca(HCO3)2
3. CaCl2
4. MgSO4
Select the correct answer using the code given below.
- A.3 and 4
- B.2 and 3
- C.1 and 4
- D.1 and 2
Show answer
Temporary hardness is caused by the bicarbonates of magnesium and calcium, Mg(HCO3)2 and Ca(HCO3)2. It is called temporary because simple boiling removes it: on heating, the soluble bicarbonates break down into insoluble carbonate or hydroxide, carbon dioxide and water, and the solid settles out.
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