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.
Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms.
Explain the terms:
(i) Speciation
(ii) Natural selection
(i) Speciation - Speciation is an evolutionary phenomenon by which new species are developed from existing ones. There are three models of speciation:
1. When the groups that evolve to be separate species are in different geographic locations and are isolated geographically from each other
2. When the groups that evolve to be separate species are geographic near and the individuals can move one species-area to others.
3. When the groups that evolve to be separate species occur together in the same geographic area.
(ii) Natural selection − Natural selection is a key mechanism in evolution.
It is a process that results in an increased survival and reproductive success of individuals that are well adjusted to the environment. The theory of natural selection was given by Charles Darwin.
Switch
