According to the assumptions underlying the two independent samples design, (a) Are two observations from the same

Question:

According to the assumptions underlying the two independent samples design,
(a) Are two observations from the same sample, say X2 and X4,
(i) Independent?
(ii) Do they always have the same distribution?
(b) Are two observations from different samples, say X2 and Y2,
(i) Independent?
(ii) Do they always have the same distribution?