The nuclear particles which are assumed to hold the nucleons together are ?
Answer: A
Mesons are held to bind the nucleons.
Yukawa predicted in 1935 that a particle of intermediate mass carries the strong nuclear force, and the pion was found in 1947. The exchange of pions between protons and neutrons is the residual effect of the colour force acting between their quarks.
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The number of d-electrons in Fe2+ (Z = 26) is not equal to that of
Answer: D
The odd one out is the p-electrons in Cl (Z = 17).
\(\mathrm{Fe^{2+}}\) is \([\mathrm{Ar}]3d^6\), so it has six d-electrons. Neon \((1s^2 2s^2 2p^6)\) has six p-electrons and magnesium \((1s^2 2s^2 2p^6 3s^2)\) six s-electrons, while neutral Fe is \([\mathrm{Ar}]3d^6 4s^2\) and also has six d-electrons. Chlorine is \(1s^2 2s^2 2p^6 3s^2 3p^5\), giving \(6+5=11\) p-electrons.
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Which one of the following can be used to confirm wether drinking water contains a gamma emitting isotope or not
Answer: B
A scintillation counter would confirm it.
Gamma photons striking a sodium iodide crystal produce flashes of light, which a photomultiplier converts into countable electrical pulses; the pulse height also identifies the emitting isotope. A microscope shows nothing of radiation, and a lead plate blocks it rather than detecting it.
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The molecules of which gas have highest speed?
Answer: A
\(\mathrm{H_2}\) at −73 °C has the highest molecular speed.
The root-mean-square speed is \[u_{rms}=\sqrt{\frac{3RT}{M}}\] so the ranking depends only on \(T/M\):
\(\mathrm{H_2}\): \(200/2=100\); \(\mathrm{CH_4}\): \(300/16=18.8\); \(\mathrm{N_2}\): \(1300/28=46.4\); \(\mathrm{O_2}\): \(273/32=8.5\).
Hydrogen's ratio is the largest by a wide margin, so its molecules are the fastest despite the low temperature.
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Which of the following is a false statement?
Answer: B
The false statement is that bond order is proportional to bond length.
The relation is inverse: the higher the bond order, the more electron density holds the nuclei together and the shorter and stronger the bond. Compare C–C at 154 pm, C=C at 134 pm and C≡C at 120 pm.
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The number of g-molecule of oxygen in 6.02 x 1024CO molecules is
Answer: C
The answer is 5 gram molecules.
\[n(\mathrm{CO}) = \frac{6.02\times10^{24}}{6.02\times10^{23}} = 10\ \text{mol}\]
Ten moles of CO contain ten moles of oxygen atoms. Since a gram molecule of oxygen is \(\mathrm{O_2}\), \[n(\mathrm{O_2}) = \frac{10}{2} = 5\ \text{mol}\]
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The main chemical constituent of clay is ?
Answer: C
Clay is chiefly aluminium silicate.
Kaolinite, \(\mathrm{Al_2Si_2O_5(OH)_4}\), forms by the weathering of feldspar. Its layered sheet structure lets the plates slide over one another when wet, which is what makes clay plastic and mouldable.
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Air contains maximum amount of
Answer: B
Air contains most nitrogen, about 78 per cent by volume.
Oxygen makes up 21 per cent, argon 0.93 per cent and carbon dioxide about 0.04 per cent. Free hydrogen is present only in traces, being light enough to escape into space.
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An alloy is
Answer: D
An alloy is a mixture.
It is a homogeneous mixture of two or more metals, or of a metal with a non-metal, in no fixed proportion - brass may be 60–90 per cent copper. Because the composition can vary, an alloy is not a compound.
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Which is the Lightest of all the metals?
Answer: B
Lithium is the lightest metal, with a density of \(0.53\ \mathrm{g\,cm^{-3}}\).
It is only about half as dense as water, so it floats on it - as do sodium (0.97) and potassium (0.86). Hydrogen is lighter still but is a non-metal under ordinary conditions.
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