Hello!
The answer is:
The second option,
![(\sqrt[m]{x^(a) } )^(b)=\sqrt[m]{x^(ab) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/bvarht4rufhv9cty2ioupo19q9z1cg6zbu.png)
Why?
Discarding each given option in order to find the correct one, we have:
First option,
![\sqrt[m]{x}\sqrt[m]{y}=\sqrt[2m]{xy}](https://img.qammunity.org/2020/formulas/mathematics/high-school/btrryptug4gukjuq6f8i34so8wrjvpqxqb.png)
The statement is false, the correct form of the statement (according to the property of roots) is:
![\sqrt[m]{x}\sqrt[m]{y}=\sqrt[m]{xy}](https://img.qammunity.org/2020/formulas/mathematics/high-school/fn8ty4ih1joxu06w9hujmqow1z3pdvxv21.png)
Second option,
![(\sqrt[m]{x^(a) } )^(b)=\sqrt[m]{x^(ab) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/bvarht4rufhv9cty2ioupo19q9z1cg6zbu.png)
The statement is true, we can prove it by using the following properties of exponents:

![\sqrt[n]{x^(m) }=x^{(m)/(n) }](https://img.qammunity.org/2020/formulas/mathematics/middle-school/qgs0ck9lcsi6vi15h5rc6g7byse9pqfzub.png)
We are given the expression:
![(\sqrt[m]{x^(a) } )^(b)](https://img.qammunity.org/2020/formulas/mathematics/high-school/xoa1rn6bt0tr5exg9gq9k99qm8hhixl5r9.png)
So, applying the properties, we have:
![(\sqrt[m]{x^(a) } )^(b)=(x^{(a)/(m)})^(b)=x^{(ab)/(m)}\\\\x^{(ab)/(m)}=\sqrt[m]{x^(ab) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/b91mf4e119e1nyolvvw9ie46rafr0ewe5l.png)
Hence,
![(\sqrt[m]{x^(a) } )^(b)=\sqrt[m]{x^(ab) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/bvarht4rufhv9cty2ioupo19q9z1cg6zbu.png)
Third option,
![a\sqrt[n]{x}+b\sqrt[n]{x}=ab\sqrt[n]{x}](https://img.qammunity.org/2020/formulas/mathematics/high-school/kqh5pe1vzmqm37z92dbqi8n215rwtw5zxf.png)
The statement is false, the correct form of the statement (according to the property of roots) is:
![a\sqrt[n]{x}+b\sqrt[n]{x}=(a+b)\sqrt[n]{x}](https://img.qammunity.org/2020/formulas/mathematics/high-school/1gqgta6bp5m8eerni09hjd6mp8hl0bkws2.png)
Fourth option,
![\frac{\sqrt[m]{x} }{\sqrt[m]{y}}=m√(xy)](https://img.qammunity.org/2020/formulas/mathematics/high-school/c9oipquit5d9lpjouygq0gi6iuyji2hgys.png)
The statement is false, the correct form of the statement (according to the property of roots) is:
![\frac{\sqrt[m]{x} }{\sqrt[m]{y}}=\sqrt[m]{(x)/(y) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/w3zcu1so6m3yu26jbluc0572o4aars0ejr.png)
Hence, the answer is, the statement that is true is the second statement:
![(\sqrt[m]{x^(a) } )^(b)=\sqrt[m]{x^(ab) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/bvarht4rufhv9cty2ioupo19q9z1cg6zbu.png)
Have a nice day!