Unit digit of a square of a number is equal to the unit digit of square of unit digit of that number.
So,
(i)81
 - Unit digit of square of 81
 will be 1
.
(ii)272
 - Unit digit of square of 272
 will be 4
.
(iii)799
 - Unit digit of square of  799
  will be 1
.
(iv)3853
 - Unit digit of square of 3853
 will be 9
.
(v)1234
 - Unit digit of square of 1234
 will be 6
.
(vi)26387
 - Unit digit of square of 26387
 will be 9
.
(vii)52698
 - Unit digit of square of 52698
 will be 4
.
(viii)99880
 - Unit digit of square of 99880
 will be 0
.
(ix)12796
 - Unit digit of square of 12796
 will be 6
.
(x)55555
 - Unit digit of square of 55555
 will be 5
.