This boils down to the concept of Binary digits. Take an 
array size of 64 for example. We start from 0 and end at 
63. We require 6 bits.But, if we were to start from 1 and 
end at 64, we would require 7 bits to store the same 
number, thus increasing the storage size.

the index of array, which is of the form a[i], is converted 
by the compiler in the form [a+i]. So, the index of first 
element is zero because [a+0] will give 'a' & the first 
array element can be accessed. Due to this, we can also 
access the array elements as'i[a]' instead of 'a[i]' , & 
this will not produce an error.

i think 2nd answer is correct
'we can also 
access the array elements as'i[a]' instead of 'a[i]' , & 
this will not produce an error' is wrong

Both Answer ARE correct but First one is EXACT and after 
that compiler is design according to that