(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.
There are different layers in the atmosphere. Due to the variation of density in the atmospheric medium, refraction takes place. The atmosphere bends the starlight towards the normal. Hence, the star appears slightly higher from the horizon. This apparent positioning is not stationary but keeps changing.
Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms.