Thank you for the opportunity to help you with your question!
The null and alternative hypothesis are mutually exclusive
because the alternative hypothesis is really the replacement to the null
hypothesis if the null hypothesis is not valid.
The null hypothesis states that a population parameter is
equal to a value. The null hypothesis is often an initial claim that researchers specify using
previous research or
The alternative hypothesis states that the population
parameter is different than the value of the population parameter in the null
hypothesis. The alternative hypothesis
is really the backup to the null hypothesis if the null hypothesis is invalid.
Therefore, the two hypotheses need to be mutually exclusive.
Please let me know if you need any clarification. I'm always happy to answer your questions.