They produce hydrogen gas when reacted with metals
Independent variable: FERTILIZER.
This is the variable that you think affect your dependent variable and so you change it and use different types of it to confirm your prediction.
Dependent variable: COLOR.
That is the variable you are interested in.
Hypothesis: THE TYPE OF FERTILIZER USED IN CULTIVATING HYDRANGEA FLOWER AFFECT THEIR COLOR.
An hypothesis is a generalized statement which predicts the relationship between the variables you are examining.
Control group: THE GROUP THAT DID NOT GET ANY FERTILIZER
The control group is the group that does not receive any treatment.
Experimental groups: THE GROUPS THAT RECEIVED FERTILIZERS.
The experimental group is the group that receives treatment.
Constants: TYPES OF SOIL USED, MORNING SUNLIGHT, WATER AND THE NO OF DAY THE EXPERIMENT LAST.
The constants are the inputs into your experiment which you give to all the groups.