The number of grams of agarose that you need to make 200 ml of 2% agarose gel is 4 grams
calculation
number of grams is calculated using M/v x100 =% m/v formula
M (mass) =?
V(volume) = 200 ml
%(M/V) = 2%
convert the 2 % M/V into fraction = 2/100
then substitute the values into the equation
= M/200 ml = 2/100
multiply both side by 200
M is therefore = 2/100 x200
M=4 grams