Figures Y and X above are of:

The correct answer is Option (4) → Electrostatic precipitator and scrubber respectively

Option (1) Scrubber and smoke screen respectively — Incorrect. Figure Y has electrode wires and collecting plates that charge and collect dust; that is the electrostatic precipitator, not a scrubber. A smoke screen is not a pollution-control device described in NCERT.

Option (2) Exhaust of a power plant and smoke screen respectively — Incorrect. An exhaust is only the waste gas leaving a plant; Figure Y is a device that cleans it. Figure X, with its spray of water or lime, is the scrubber, not a smoke screen.

Option (3) Scrubber and electrostatic precipitation respectively — Incorrect. Figure Y is the precipitator and Figure X the scrubber, not the other way round.

Option (4) Electrostatic precipitator and scrubber respectively — Correct. In figure Y, dust particles are given a charge and collected on plates: the electrostatic precipitator. In figure X, the polluted gas passes through a spray of water or lime: the scrubber, which removes gases like sulphur dioxide.

Note: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Air Pollution and Its Control – “… There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator (Figure 16.1), which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant. It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall. A scrubber (Figure 16.1) can remove gases like sulphur dioxide. In a scrubber, the exhaust is passed through a spray of water or lime.”