<u>Answer: </u>The correct answer is Option D.
<u>Explanation:</u>
Elements which belong to same group show similar chemical properties because they have same number of valence electrons.
From the given options:
<u>Option A:</u> Cobalt belongs to Group 9, Iron belongs to Group 8 and Nickel belongs to Group 10. Hence, they will not show similar chemical properties.
<u>Option B:</u> Iron belongs to Group 8, Copper belongs to Group 11 and Ruthenium belongs to Group 8. Hence, they will not show similar chemical properties.
<u>Option C:</u> Ruthenium belongs to Group 8, Iridium belongs to Group 9 and Palladium belongs to Group 10. Hence, they will not show similar chemical properties.
<u>Option D:</u> Gold, Silver and Copper belongs to the same group which is Group 11. Hence, they all will show similar chemical properties.
Thus, the correct answer is Option D.