21.
The gas produced in marshy places due to decomposition of vegetation is

22.
Organic compounds are

23.
Vinegar is an aqueous solution of

24.
Two elements which can form a large number of compounds are

25.
Alcoholic (– OH) group can be identified by :

26.
Which one is the simplest form of alkane?

27.
Which of the following is not a natural source of hydrocarbon?

28.
The element with highest first ionisation energy is

29.
In a period from Li to F, ionisation potential

30.
In the periodic table of elements, on moving from left to right across a period, the atomic radius