How many pairs of chromosomes are present in human beings (in $pairs$)?

In human males,all the chromosomes are paired perfectly except one. These unpaired chromosomes are:
$(i)$ Large chromosome
$(ii)$ Small chromosome
$(iii)$ $Y-$ chromosome
$(iv)$ $X-$ chromosome

$(a)$ Differentiate between:
$(i)$ Homologous organs and Analogous organs
$(ii)$ Pollination and Fertilisation
$(b)$ What do fossils tell us about the process of evolution?

List three main factors responsible for the speciation and briefly describe each one of them.

From the list given below,select the character which can be acquired but not inherited.

Why did Mendel choose the pea plant $(Pisum \text{ } sativum)$ for his experiments?