fix grammar
The experiment consist independent variable is (Na2S2O3)and dependent variable is time taken for cross to disappear.
do not go voer 16 words
The experiment consists of an independent variable, which is (Na2S2O3), and a dependent variable, which is the time taken for the cross to disappear.
To fix the grammar, you can rephrase the sentence as follows:
"The experiment consists of an independent variable (Na2S2O3) and a dependent variable, which is the time taken for the cross to disappear." (16 words)