The nitrogen atom has 7 protons and 7 electrons. The nitride ion will have
Answer: B
The nitride ion has 7 protons and 10 electrons.
Forming \(\mathrm{N^{3-}}\) means gaining three electrons to reach the neon configuration. The number of protons never changes in ion formation - changing it would change the element - so only the electron count moves, from 7 to 10.
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Which one of the following substances does not have a melting point
Answer: D
Glass has no melting point.
It is an amorphous solid - a supercooled liquid - with no long-range order and therefore no fixed temperature at which the lattice collapses. It simply softens gradually over a range. Crystalline solids such as sodium chloride, and the elements bromine and mercury, all have sharp melting points.
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The main chemical constituent of the oil of cardamom which is responsible for flavour of this oil is
Answer: A
Cineole, also called eucalyptol, gives cardamom oil its flavour.
It makes up a large part of the volatile oil of the seeds, alongside \(\alpha\)-terpinyl acetate. Eugenol is the principal constituent of clove oil, geraniol of rose and citronella oils, and limonene of citrus peel.
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Artificial radioactivity elements are present in
Answer: D
Artificially produced radioactive elements belong to the f-block.
Every element beyond uranium is man-made, and neptunium through lawrencium are actinides, which are f-block elements. They are produced by neutron capture in reactors or by bombardment in accelerators.
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The metal used to recover copper from a solution of copper sulphate is ?
Answer: A
Iron recovers copper from copper sulphate solution.
\[\mathrm{Fe + CuSO_4 \rightarrow FeSO_4 + Cu}\] Iron is above copper in the reactivity series, so it reduces \(\mathrm{Cu^{2+}}\) to the metal. Silver and mercury lie below copper and cannot; sodium would attack the water first.
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Nucleus of Hydrogen atom consists of
Answer: C
The nucleus of an ordinary hydrogen atom is a single proton.
Protium is the only nuclide with no neutron at all. This is why the hydrogen ion \(\mathrm{H^+}\) is simply a bare proton, and why it cannot exist free in water.
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The nuclear particles which are assumed to hold the nucleons together are
Answer: D
Mesons are held to bind the nucleons together.
Yukawa proposed in 1935 that the strong nuclear force is carried by an exchange particle of intermediate mass; the pi-meson, or pion, was found in cosmic rays in 1947 and matched his prediction. In modern terms the pion exchange is the residual effect of the colour force between quarks.
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Which one of the following directly explains the law of conservation of mass?
Answer: C
Dalton's atomic theory explains the conservation of mass.
Its postulate is that atoms are indivisible and are neither created nor destroyed in a chemical reaction; a reaction only rearranges them. Since the same atoms are present before and after, the total mass cannot change.
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How many moles are there in 140g of Si (atomic mass of silicon is 28)
Answer: A
There are 5 moles.
\[n = \frac{\text{mass}}{\text{molar mass}} = \frac{140}{28} = 5\ \text{mol}\]
which is \(5 \times 6.022\times10^{23} = 3.01\times10^{24}\) silicon atoms.
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The monomer of polythene is
Answer: B
The monomer of polythene is ethylene (ethene), \(\mathrm{CH_2{=}CH_2}\).
Under high pressure with a peroxide initiator, or over a Ziegler–Natta catalyst, the double bonds open and the units join end to end in an addition polymerisation. Vinyl chloride is the monomer of PVC.
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