1 – All individuals within a species show variation. e.g. All humans have some sort of variation in our genes such, as different eye colour or faces. So 1 is correct.
2 – Competition between individuals within a species is called intraspecific competition (intra=within). e.g. Lions have to compete with other lions for food.
3 – This is true. Let us explain this with an example. Let us take the cubs of a lion. The cubs which are more tolerant of higher temperatures will more likely be able to survive for a longer period of time. On the other hand, if a cub, born with genes which are not tolerant of high temperatures will be more likely to die earlier than the other cubs.
4 – This is not necessarily true. Individuals who have disadvantageous adaptations will also be able to breed. 4 is wrong.
5 – This is true.