Read the following passage and answer the questions based on it.

The transition metals are very hard and have low volatility. Their melting and boiling points are high. In any row, the melting points of these metals rise to a maximum at $d^5$ and fall regularly as atomic number increases. The high melting points of these metals are attributed to the involvement of greater number of electrons from (n-1)d in addition to ns electrons in the interatomic metallic bonding.

Which is the hardest metal?

Cu

The correct answer is Option (2) → Cu.

To determine which of the metals listed (Zinc (Zn), Copper (Cu), Mercury (Hg), and Cadmium (Cd)) is the hardest, we can look at their relative hardness as defined by the Mohs hardness scale or other relevant measures.

Hardness of Each Metal

1. Zinc (Zn)

Zinc is relatively soft compared to other metals. Its hardness is around 2.5 on the Mohs scale. It is brittle at room temperature but becomes more malleable when heated.

2. Copper (Cu)

Copper has a hardness of about 3 on the Mohs scale. It is tougher than zinc and has good malleability and ductility. Copper is widely used for electrical wiring due to its excellent conductivity.

3. Mercury (Hg)

Mercury is the only metal that is liquid at room temperature, and it is very soft with a hardness of about 1.5 on the Mohs scale. Its liquid state and softness limit its hardness significantly.

4. Cadmium (Cd)

Cadmium is softer than zinc, with a hardness of about 2.0 on the Mohs scale. Cadmium is often used for electroplating and as a stabilizer in plastics.

Conclusion

Based on the hardness values: Hardest Metal: Copper (Cu), with a hardness of approximately 3 on the Mohs scale, is the hardest among the options provided.

So the correct answer is: Cu (Copper).