(c) Given, S=2n+3n For n = 1, S=21+31=5 It is not a square of rational number. For n = 2, S=22+32=4+9=13 It is not a square of rational number. For n = 3, S=23+33=8+27=35 It is not a square of rational number. For n = 4, S=24+34=16+81=97 It is not a square of rational number,