Seems to be correct.

I agree, I don’t see anything wrong with that.

Ribosomes are rather tiny, only something like max 30 nm in diameter in eukaryotes and bit smaller in prokaryotes. Chromosomes are considerably larger – so large that when condensed you can see eukaryote chromosomes easily with a light microscope. And to see them in a light microscope they need to be bigger than the wavelength of visible light – which is about 380 nm at its lowest end. Bacterial chromosomes are smaller, but still larger than ribosomes.

I know that ribosomes are composed of few RNAs and several proteins, but the hemoglobin gene, to my knowledge, is quite huge (I think it contains several very long introns, doesn’t it?). Cannot it be bigger than ribosome?

Well, for starters there are several "haemoglobin genes" (e.g. genes for the alpha chains and beta globins) in humans to begin with, and as the original question does not tell us which gene exactly is in question, I assume that the main idea of the question is to demonstrate that a gene is normally larger than its corresponding mRNA product, but smaller than some other structures, such as a ribosome.

Furthermore, a haemoglobin unit consists of several subunits which are all products of their corresponding genes, and even the fully assembled haemoglobin protein is smaller than a ribosome, so I think it is safe to assume that the genes for encoding those subunits are also smaller than ribosomes.

Unless I’m mistaken, a whole haemoglobin unit has a diameter of roughly 10 nm, so it is about three times smaller in size than a ribosome. And a gene for any given haemoglobin subunit is likely to be smaller than this even if it had long introns, I assume.

I guess so. Just that in all the animations are the ribosomes so small 😆

Yeah, I guess they can be considered rather tiny even on a cellular scale, since most cells can contain thousands of them or more.