Common nouns name general things, whereas proper nouns name
specific individuals or things. For example, 'man' is a common noun whereas Thomas
is a proper noun, a specific name for a particular man. Proper nouns always begin with a capital letter.
Option
A: 'Things', 'world' and 'atoms' are general names for things. Also, common nouns begin with small letters 't', 'w' and 'a'. (An exception: in any sentence or a phrase in a new
line, the first letter of the first word is a capital.)
Hence they are common nouns.
So, this option is the right
one.
Options B, C and D: 'All' is a determiner that comes before articles, nouns or numbers. It isn't a noun.
Proper nouns begin
with capital letters 'T', 'W' and 'A' whereas the nouns here begin with small letters 't', 'w' and 'a'.
Hence options B, C and D are incorrect.