The following Procedure should be followed when calculating the number of vibrational modes:-
Identify if the given molecule is either linear or non-linear
Calculate the number of atoms present in your molecule
Place the value of n in the formula and solve.
SO2 is a non-linear molecule because it contains a lone pair which causes the molecule to bent in shape hence, The mathematical formula for calculating the number of non-linear molecule in a infrared region is (3n - 6) here n is the number of atoms in molecule.
hence for Sulphur Dioxide (SO2), n will be 3
<u> Therefore, The number of lines possible for SO2 is (3*3) - 6 = 3</u>
