The null hypothesis is usually the default statement. The alternative is the opposite of the null and usually tested against the null hypothesis
In this case study,
The null hypothesis in would be that the mean time between clicks of the second hand on a particular clock is 1 second. In symbolic form it would be u = 1
The alternative hypothesis would be that the mean time between clicks of the second hand on a particular clock is 1 not second. In symbolic form, it would be: u =/ 1