Chromosomes come in pairs. We have two of each chromosomes. In other words we have 46 chromosome, or 23 pairs of them. The reason they are counted as pairs is that the two chromosomes in each pair is almost identical to the other. They have the same genes in the same order, but they will have different alleles (variations) of those genes.
And compared to other great apes it does look as if we are missing a pair of chromosomes since we have one fewer pair than they do.
But there is an answer. Scientists know that related species, some off them very closely related, can have a different number of chromosomes. That is because chromosomes can split or join. Zebras for example can have from 32 to 46 chromosomes. Horses have 64 or 66 chromosomes. Many of these can interbreed, though the offspring tend to be streile:
en.wikipedia.org
The point is that in our chromosome number 2, and there are two of them, we can find where the join is. Two of our chromosomes fused in the past. We can see the remnants of the telomeres and centromeres within the chromosome.