Which sample of matter represents a mixture?

A mixture is a new substance that you get when you mix two or more different substances together and blend them so you either create a homogeneous mixture, or a heterogeneous one. In you case (assuming that your choices are aqueous ammonia, liquid mercury, gaseous ethane, solid iodine), the correct answer is aqueous ammonia, given that it is a mixture of ammonia and water, whereas the other options are not mixtures because they only consist of one element.

Alpha particles have positive charge, beta particles have negative charge, and answer 4 just doesn’t make sense. thus, you are left with only one possible answer.