DNA is a chemical (deoxyribonucleic acid). DNA is like a chain, and the molecule can have anywhere from 1 link to billions in that chain.
Chromosomes are structures made of long strands DNA, sometimes wound around bits of protein.
A “gene” is a unit of inheritance. The concept of genes is older than our knowledge of DNA and chromosomes. As we began to understand the role of DNA, a gene was originally understood to be a location or piece of a chromosome. Today, we tend to think of it in terms as a specific DNA sequence that’s typically part of the longer DNA molecule that makes up a chromosome.
Chromosomes are DNA, so you can’t really say one is bigger than the other. Chromosomes typically have multiple genes along their length, so we say that they contain genes.
Genes can get pretty long (the Huntington gene in humans is 180 kb long), and chromosomes can be pretty short (the human mitochondria contain 17 kb circular chromosomes), so you can’t say that chromosomes are always longer than genes. Chromosomes are longer than the genes that they contain.
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