Chapter 1 - Introduction to Chemistry - Questions and Exercises - Exercises - Page 34: 1.39

(a) element (b) heterogeneous mixture (c) homogeneous mixture (d) heterogeneous mixture

(a) element Helium is an element because it cannot be broken down any further into any constituent parts that can still be identified as helium. On the periodic table, helium is element 2 with the elemental symbol He. (b) heterogeneous mixture A muddy river is a heterogeneous mixture because it is made of different substances that are mixed together, but not in a consistent way. (c) homogeneous mixture Window glass is a homogeneous mixture because it is made of a combination of different compounds but is consistent throughout. (d) heterogeneous mixture Paint is a heterogeneous mixture because it is made of different substances but you would have to mix it up to have a consistency that is more or less uniform. If left untouched, paint will separate into its different constituent parts.