The table lists two instrument transformers and their features :

Instrument transformers		Features
		(P)	Primary is connected in parallel to the grid
(X)	Current transformer (CT)	(Q)	Open circuited secondary is not desirable
(Y)	Potential transformer (PT)	(R)	Primary current is the line current
		(S)	Secondary burden affects the primary current

The correct option is: X matches with Q and R; Y matches with P and S.

Let's analyze the characteristics of both instrument transformers to understand why this mapping is correct:

1. Current Transformer (CT) — (X):
- (R) Primary current is the line current: A current transformer is connected in series with the power line. As a result, the primary winding carries the full line current of the system.
- (Q) Open circuited secondary is not desirable: Under normal operation, the secondary current creates a counter-flux that opposes the primary flux. If the secondary is open-circuited while the primary is carrying line current, the opposing flux vanishes. The entire primary current then magnetizes the core, driving it deep into saturation. This induces a very high, dangerous voltage across the open secondary terminals, which can damage the transformer insulation and present a severe safety hazard. Therefore, an open-circuited secondary is not desirable.
Thus, X matches with Q and R.

2. Potential Transformer (PT) — (Y):
- (P) Primary is connected in parallel to the grid: A potential transformer is used for voltage measurement and protection. Its primary winding is connected in parallel (or shunt) across the power lines to measure the system voltage.
- (S) Secondary burden affects the primary current: Since the PT operates at a constant grid voltage, the current flowing through the primary winding is determined by the load or impedance (called burden) connected across the secondary terminals. Any change in the secondary burden directly changes the secondary current, which in turn alters the primary current.
Thus, Y matches with P and S.