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The Fundamental Unit of Life
What are the different stages observed when a discharge tube is connected to a high voltage source and the pressure of the air in it is reduced gradually?
The following observations are made in the discharge tube under high voltage when the air pressure is gradually reduced.
(i) At normal air pressure — No change
(ii) At slightly reduced air pressure — Unsteady light emission
(iii) At still lower pressure — Tube fills up with uniform glow with magneta-red colour
(iv) At pressure below 0.001 mm Hg — Tube appears dark and the cathode starts glowing with a faint greenish light.
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Define valency by taking examples of silicon and oxygen.
Explain with examples, (i) Atomic number, (ii) Mass number, (iii) Isotopes, and (iv) Isobars. Give any two uses of isotopes also.
Na+ has completely filled K and L-shells. Explain.
If Z = 3, what would be the valency of the element? Also, name the element.
Composition of the nuclei of two atomic species X and Y are given as under
X Y
Protons = 6 6
Neutrons= 6 6
Give the mass numbers of X and Y. What is the relation between the two species?
For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about 1/2000 times that of proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
Rutherford’s α-particle scattering experiment was responsible for the discovery of
Isotope of an element has
Number of valence electrons in Cl- ion are
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