If the diploid number in a certain animal is 16, what is the number of chromosomes in each sperm?
"Diploid" means that the organism has two copies of every chromosome. If its diploid number is 16, that means that it must have 8 distinct chromosomes.
Gametes, such as sperm and eggs, are haploid, meaning that they have one copy of each chromosome. This reduction is necessary in order for fertilization to produce a diploid organism; if the animal did not reduce its gametes from diploid to haploid form, then each subsequent generation of offspring would double the number of chromosomes they possess, which would lead to major problems.
The advantage of using the haploid reproductive technique is that it gives the organism a chance to produce entirely unique combinations of chromosomes for every gamete. As the chromosomes are segregated (meaning they are separated and distributed to the gametes) they can be shuffled, leading to combinations that can be more or less like either parent's chromosomes, or any combination of the two.
If the parent's diploid number is 16, then it's haploid number must be 8, and this is also the number of chromosomes that would be found in any of its normal sperm or egg cells.