Achemical company is developing a new fertilizer for tomatoes and wants to know if tomatoes grown with it are larger than the known mean weight of tomatoes grown with their current fertilizer, which is mean =1.2 pounds. they will feed 30 young plants with the new fertilizer and measure the mean weight of its fruits produced by the plants. state the null hypothesis and alternative hypothesis for this test.

Hello!

The null hypothesis would be that the mean weight of tomatoes grown with the new fertilizer is not different to the mean weight of tomatoes grown with the new fertilizer (1,2 pounds)

The alternative hypothesis would be that the mean weight of tomatoes grown with the new fertilizer is larger than the mean weight of tomatoes grown with the new fertilizer (1,2 pounds). 

This procedure is called a Statistical hypothesis testing. The Null hypothesis is the one that can't be rejected unless data shows that it is false, it usually involves a "no". The Alternative hypothesis is the one that you expect to prove.  It usually involves saying that a given value is different, higher or lower than the one for the null hypothesis. 

Have a nice day!