A page entry should be padded if its not in byte, for 21 bits we should add 3 bits more to make it 3B entry, isn't this is a default thing why they need to specify?
we cannot pad by default , actually here said approximate pte size so they padded
I think Page Table Entry should be padded. A similar question was asked in Gate which is as below.
(Without padding the answer would have been 1.75 MB and using padding the answer is 2 MB)
Also in many practical implementations, the Page table entry is rounded up as it is said in the below link.
Agreed, Memories are word addressable. If the entries are not padded, accessing them will be difficult as the starting point of entry will be in between somewhere in a byte and not at the beginning at byte.