This link could be useful:

https://www.researchgate.net/post/Why-is-the-dielectric-constant-for-metals-infinity

Good luck!

the answer is 1. they are not dielectric materials

Dear Siva, thank you for asking this interesting technical question. In this context please have a look at the following links which might help you in your analysis:

https://www.engineeringtoolbox.com/relative-permittivity-d_1660.html

and

What is the dielectric constant for metal?

https://www.quora.com/What-is-the-dielectric-constant-for-metal

As mentioned by Muhammad Hamza El-Saba metals like nickel and platinum are not dielectric materials:

Why can a metal not be used as a dielectric in between parallel plate capacitors?

https://www.quora.com/Why-can-a-metal-not-be-used-as-a-dielectric-in-between-parallel-plate-capacitors