Choose the incorrectly spelt word.

Correct option is D

Option (d) is the incorrectly spelt word.
Correct spelling is: Monitor – A device used for observing, checking, or keeping a continuous record. (निरीक्षण यंत्र)
Example: The teacher asked the class monitor to maintain discipline.
Meanings of all the given options:
· (a) Slope: A surface of which one end is at a higher level than the other (ढलान)
· (b) Constant: Occurring continuously over a period of time (लगातार)
· (c) Chemical: A distinct compound or substance (रासायनिक पदार्थ)