III. Very short answer type questions:                                                    9 X 1 =  9 21.  Name the chemicals that are used to remove weeds.

22. Write the name of bacteria that helps in the formation of curd.

23.  which cell does not have nucleus?

24. Name some artificial fibres

25.  Name the element present in coal

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26.  What is the unit for expressing the calorific value of a fuel?

27. What is meant by atmospheric pressure?

28.Name the device which work on the principle of multiple reflection

29. which part of the cells contains organelles please ​