Starting with the first one
#color(blue)((1))# One mole of any substance contains exactly #6.022 * 10^(23)# molecules or atoms of that substance - this is known as Avogadro's number. Since you have less than 1 mole of ethanol, #CH_3OH#, you'll get less that #6.022 * 10^(23)# molecules of ethanol.
#3.10 * 10^(-2)cancel("moles") * (6.022 * 10^(23)"molec.")/(1cancel("mole")) = color(green)(1.87 * 10^(22)"molec.")#
#color(blue)((2))# To get the number of carbon atoms present in that much butane, you must first determine how many molecules of butane you're dealing with. Since the molecular formula of butane is #C_4H_10#, you'll get 4 carbon atoms for every 1 molecule of butane.
#0.570cancel("moles") * (6.022 * 10^(23)"molec.")/(1cancel("mole")) = 3.43 * 10^(23)"molec."#
Therefore, you get
#3.43 * 10^(23)cancel("molecules") * ("4 C atoms")/(1cancel("molecule")) = color(green)(1.37 * 10^(24)"atoms"#
Questions #color(blue)((3))# and #color(blue)((4))# are identical to the first two, the only difference being the actual values you have to work with.
For question #color(blue)((4))#, the number of atoms of oxygen in aluminium nitrate will be 9. You get 3 oxygen atoms from each of the 3 nitrate anions that make up the compound.
