Question

Which of these is an unbiased sampling to find out what whether people have 3D television at home?

Ask people who have just seen a demonstration of 3d television.
Ask the first ten customers who buy a 3D television.
Ask every tenth customer at an electronics store.
Ask every tenth passer-by on the street.

would it be the third option? since its not biased

Answer 1

or would it be biased because its in the store?

Answer 2

It should be the passer-bys. There is bias in asking the electronics store customers because it is in a store, and that isn't an accurate representation of a whole population.