which pair(s) of liquids will be miscible ?

Question

H2O AND CH3CH2CH2CH2CH3(PENTANE)
C6H6 (BENZENE) AND CCl4(CHLOROFORM)
C2H5OH (ETHANOL) AND CH3COOH(ACETIC ACID)

how do you know if they are miscible?

Answer 1

Generally you go by the rule that "like dissolves like."
Water is polar, acetic acid is polar and ethanol is polar (and it contains OH groups).
You would expect ethanol and acetic acid to be miscible. The same is true for benzene and CCl4 (both non-polar). You would not expect H2O (polar) and pentane (non-polar)to be miscible.