Can u give me any tip on deciding the null and alternative hypothesis in hypothesis testing?

Assuming that you are doing an experiment, the null hypothesis is that there will be no difference between the control and experimental data. The idea is to show that there is a significant difference (usually at the 95% level) between the two (alternative hypothesis), thereby disproving the null hypothesis. Remember that you can never prove anything in science, only disprove. The null hypothesis is the one you attempt to disprove.