Short Answer Type(i) How do you calculate the possible valency of an element from the electronic configuration of its atoms?
(ii) Calculate the valency of element X whose atomic number is 9.
On the basis of electronic configuration, how will you identify the first and the last element of a period?
The stars appear higher from the horizon than they actually are. Explain why it is so.
Explain why the planets do not twinkle but the stars twinkle.
Planets are closer to the earth and do not appear to be point sources of light. They are considered to be extended sources of light. If a collection of a large number of point-sized sources of light is considered, then the total variation in the amount of light entering our eye from all the individual point sized sources will average out to zero, nullifying the twinkling effect.
Stars, on the other hand, are point-sized objects and twinkle by atmospheric refraction of light.
Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms.
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