What is meant by the term 'Darwinian fitness'?

Which one of the following is $INCORRECT$ with respect to genetic drift?

The concept that "Population tends to increase geometrically while food supply increases arithmetically" was put forward by:

In a gene pool,along with beneficial mutations,those mutations also exist which are damaging to an individual. It has been found that these mutations are often not eliminated from the population because:
$I.$ They have survival value.
$II.$ They are acquired.
$III.$ They are recessive and carried by heterozygous individuals.
$IV.$ They show genetic drift.
Choose the incorrect option$(s)$ regarding why these mutations persist in the gene pool.

How did Darwin explain the origin of species?

Which of the following was not proposed by Darwin in his theory of evolution?