Complementary distribution is the distribution of phones in their respective phonetic environments in which one phone never appears in the same phonetic context as the other. ... For example, English [h] and [ŋ] are in complementary distribution: [h] occurs only at the beginning of a syllable and [ŋ] only at the end.

Are allophones in complementary distribution?

Allophones usually appear in complementary distribution, that is, a given allophone of one phoneme appears in one predictable environment, but the other allophones of that phoneme never appear in that environment.

How can you tell when two sounds are in complementary distribution?

Two classes of sounds are in complementary distribution if there is a context such that one class only occurs there and the other class can't occur there. For English speakers, aspirated [pH] and unaspirated [p] seem like slightly different versions of the same sound.