Determine the correctness or otherwise of the following Assertion $[\text{a}]$ and the Reason $\text{[r]}$.
Assertion $\text{[a]}$: Chromosome mutations can change the structure of chromosomes.
Reason $\text{[r]}$ : All chromosome mutations arise due to nondisjunction of chromosomes during mitosis or meiosis.
- Both $\text{[a]}$ and $\text{[r]}$ are false
- $\text{[a]}$ is true but $\text{[r]}$ is false
- Both $\text{[a]}$ and $[\mathrm{r}]$ are true and $[\mathrm{r}]$ is the correct reason for $\text{[a]}$
- Both $\text{[a]}$ and $[\mathrm{r}]$ are true but $[\mathrm{r}]$ is not the correct reason for $\text{[a]}$