Step 1: Take the honeybee as a working example.
In a beehive, the queen mates and stores sperm. She can choose to fertilize an egg or let it develop without fertilization.
Step 2: Follow the two possible outcomes.
If she fertilizes the egg, it gets two sets of chromosomes and grows into a female, a worker or a new queen. If she leaves the egg unfertilized, it has only one set of chromosomes and grows into a male drone.
Step 3: See what is really deciding the sex.
The deciding factor is not fertilization by itself, it is how many sets of chromosomes the resulting individual ends up with. Fertilization is only the mechanism that produces that chromosome number difference.
Step 4: Test the other statements against this.
Saying fertilized eggs become males, or unfertilized eggs become females, or that females are haploid and males diploid, all get the pairing backward from what actually happens in bees and ants.
Final Answer:
In haplodiploidy, sex is fixed by the number of chromosome sets an individual carries, option (1).