The given expression in simplified form are:
1) \(\sqrt[7]{12} =12 ^{\frac{1}{7}}\)
2)\((\sqrt[7]{3})^{4} =3^{\frac{4}{7}}\)
3) \(\sqrt[7]{81} =81^{\frac{1}{7}} =3^{\frac{4}{7}}\)
4)\(\sqrt[4]{21} =21^{\frac{1}{4}}\)
5) \(\sqrt[4]{3^{7}} =3^{\frac{7}{4}}\)
6)\(\sqrt[4]{3^{7}} =3^{\frac{7}{4}}\)
Among all the options option 2 and 3 are the right one.
