a) Table salt: it is a compound. A compound is a combination of atoms in fixed proportions.Table salt is NaCl, which means that table salt is a compound of 1 atom of Na and 1 atom of Cl and not other thing. b) Blood: is an homogeneous mixture: it is a mixture of many compounds which can not be easily distinguished or separated, you need microscopes or very special physical methods to distinguish or separate the different compounds of blood. d) Steel: it is a special king of homogeneous mixture (it is called an alloy) which, as in the case of blood, cannot be distinguished or separated easily. d) Planet earth: it is a heterogeneous mixture. You can easily distinguish many of the compounds of the planet Earth: water, oxygen, carbon,...