(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?
State the two laws of reflection of light.
Laws of reflection states that:
i. The angle of incidence is equal to the angle of reflection.
ii. The incident ray, the reflected ray and the normal to the mirror, all lie in the same plane.
The stars appear higher from the horizon than they actually are. Explain why it is so.
Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms.