A set of elements is finite if its number of elements is not infinite. So basically if we can give a number that is equal to the size of the set then that set is finite. Let's see each case:
First we have "All whole numbers". There's an infinite amount of whole numbers. Every time you think about a whole number there is also one that is bigger and another one that is smaller. This happens to any whole number that you come up with therefore this is not a finite set.
Second we have "All natural numbers less than 100,000". The natural numbers are all the positive whole numbers plus the zero. There are 100,000 natural numbers less than 100,000: 0, 1, 2... ,99998 ,99999. Since the size of the set isn't infinite then this is a finite set.
Third we have "All letters of the alphabet". Although it varies depending on the countrie, the latin alphabet (the one used in english) has around 26 different letters. This means that the size of this set is not infinite therefore this set is finite.
Fourth we have "All odd numbers". Just like what happens with the first set every time you think about an odd number there is also one that is bigger and another one that is smaller. Therefore there are infinite odd numbers and the set is not finite.
Fifth we have "All the world's population". There are approximately 8,000,000,000 people in the earth which is a defined number (not an infinite). Then this set is finite.
Sixth we have "∅" which is known as the empty set. As its name indicates this set has no elements which means that its size is equal to 0. Since its size is not infinite then this is a finite set.
In summary, the correct options are:
-All natural numbers less than 100,000.
-All letters of the alphabet.
-All the world's population
-∅