The correct option is
C Bird
In order to choose a noun that does not belong to the group, we must understand what nouns are.Nouns are naming words. For example: 'Ram is a boy.' Here, both 'Ram' and 'boy' are nouns. 'Ram' is a proper noun and 'boy' is a common noun. There are different types of nouns; i.e.; proper nouns, common nouns, material nouns, abstract nouns, concrete nouns, countable nouns, uncountable nouns, compound nouns and collective nouns.
Options A, B and C are all collective nouns, whereas option D is a common noun.
Option A - Bundle is a collective noun. Hence, option A is incorrect.
Option B - Flock is a collective noun. Hence, option B is incorrect.
Option C - Crowd is a collective noun. Hence, option C is incorrect.
Option D - Bird is a common noun as it is not a specific bird. Hence, it doesn't belong to the group. Thus option D is the correct answer.