Hint: Start by converting both the parts of the ratio to the same unit either to litre or millilitre.
Complete step-by-step answer:
Let us first know what a ratio is.
A ratio, in basic words, is a quantity used to define a comparison between two quantities. A bit toward the advanced side, it is the quantity that defines how many times of one quantity is that of others.
At our level, apart from the definition, we will treat it as a simple fraction that defines a relation between two given quantities.
Now, starting with the solution to the above question, first moving to the conversion of 2 litre to ml.
We know that 1 litre is equal to 1000 ml. Then we can say that 2 litre is equal to $1000\times 2=2000ml$
We will now try to find the ratio of 200 ml to 2 litre.
The above ratio can also be written as 1:10.
So, the ratio of 200 ml to 2 litre is 1:10, i.e. the correct answer is option (b) 1:10
Note: Read the question carefully as in the question, including ratio, there is always a chance that the question might have a twist hidden in the words of the question. Also, it is preferred to convert the quantities to the smaller unit of the two units as this ensures that none of the numbers are in decimal form, simplifying the calculations.