Answer: Options Third, Second , Fourth are correct.
Step-by-step explanation:
Since we have given that
[tex]6x^2\\\\9x^8\\\\16x^9\\\\25x^{12}\\\\36x^{16}[/tex]
Since we know that
9, 16, 25, 36 are perfect squares.
So, we get that
[tex]9x^8=(3x^4)^2\\\\25x^{12}=(5x^6)^2\\\\36x^{16}=(6x^8)^2[/tex]
Hence, Options Third, Second , Fourth are correct.