A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture.
So the answer should be the third one. A cookie made from flour, eggs, sugar, butter and chocolate chips. The fact that you can see the chocolate chips from the cookie and you can remove it means it is a heterogeneous mixture.
Sugar and flavorings dissolved in water are a homogenous mixture because you cannot tell the different phases, the sugar and favorings are dissolved. But if it was sand and water, then it would be heterogenous.
Melted copper and zinc form an alloy, all alloys are homogeneous.
Cool air mixed with warm moist air is heterogenous, mist and fog can be considered heterogeneous mixtures, as tiny droplets of water hang visibly in the air.