The correct answer is D.
The turn ratio of a transformer is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. In this case, the turn ratio is 1:2. This means that for every turn in the primary winding, there are two turns in the secondary winding.
The voltage across a transformer winding is proportional to the number of turns in the winding. So, if the primary winding has 10 turns and the secondary winding has 20 turns, then the voltage across the secondary winding will be twice the voltage across the primary winding.
In this case, the primary voltage is 200 V. So, the secondary voltage will be 400 V.
The current in a transformer winding is inversely proportional to the number of turns in the winding. So, if the primary winding has 10 turns and the secondary winding has 20 turns, then the current in the secondary winding will be half the current in the primary winding.
In this case, the primary current is 10 A. So, the secondary current will be 5 A.
The power rating of a transformer is the product of the primary voltage and the primary current. So, the power rating of this transformer is 200 V x 10 A = 2 kW.
Therefore, the statement that is incorrect is D. The secondary current is not 20 A. It is 5 A.