Question

Which transition metal is liquid at room temperature?

• A. Hg
• B. Cu
• C. Ag
• D. Au
• A. Zn
• B. Cu
• C. Hg
• D. Cd
• A. Ti
• B. V
• C. Cr
• D. Mn
• A. Hf
• B. Ta
• C. W
• D. Re
• A. One
• B. Six
• C. Five
• D. Eight

Answer 1

The Correct Option is A

Among the transition metals, mercury (Hg) is unique because it is a liquid at room temperature. While most transition metals are solid due to their significantly high melting points, mercury's melting point is −38.83 °C, which makes it the only metal in the transition series that is liquid at room temperature. This anomaly is attributed to its electronic configuration, which causes weaker metallic bonding compared to other metals in the same category. Mercury's singular behavior in this regard distinguishes it from its counterparts such as copper (Cu), silver (Ag), and gold (Au), all of which are solid at room temperature with considerably higher melting points.

Answer 2

The hardest metal among the options provided is Cu (Copper). According to the passage, transition metals are very hard and possess high melting and boiling points because of their metallic bonding involving ns electrons and (n-1)d electrons. Copper, being a transition metal, fits this description. Metallic bonding strength generally increases with the involvement of more d electrons, which contributes to the hardness and higher melting points observed in these metals.

Answer 3

The passage explains that in a row of transition metals, the melting points typically rise to a maximum at the d⁵ electron configuration, then decrease as the atomic number increases. This trend is generally observed among the transition metals due to the increasing number of d-electrons contributing to metallic bonding.

However, manganese (Mn) is an exception to this rule. While one might expect Mn with its d⁵ configuration to have the highest melting point among its row of transition metals, it does not. The unique electronic structure of manganese causes a different behavior in its bonding properties, leading to a deviation from this generalization.

Therefore, in the context of this question, the transition metal that is an exception to the rule that melting points rise to a maximum at d⁵ is Mn (Manganese).

Answer 4

To determine which transition metal has the highest melting point, we evaluate the options based on the general trend that within a transition series, melting points rise to a peak typically around the middle of the d-block, often at or near the d5 configuration, due to the involvement of more electrons in metallic bonding. 

Among the given options, Tungsten (W) is well-known for having one of the highest melting points of all metals due to its strong metallic bonds formed by the contribution of d-electrons. Specifically, the melting point of W is approximately 3422°C (6192°F), making it the transition metal with the highest melting point in the periodic table, surpassing Hafnium (Hf), Tantalum (Ta), and Rhenium (Re).

Therefore, based on the melting point and bonding considerations, the transition metal with the highest melting point is:

W (Tungsten)

Answer 5

To determine how many electrons are needed in the reduction of \(Cr_{2}O_{7}^{2-}\) to \(Cr^{3+}\), we will consider the change in oxidation states and balance the redox reaction. The process involves: 

1. Identifying Oxidation States: In \(Cr_{2}O_{7}^{2-}\), each chromium (Cr) has an oxidation state of +6. In \(Cr^{3+}\), the oxidation state is +3.
2. Change in Oxidation State: The reduction is from +6 to +3 for each Cr atom.
3. Balancing the Reduction Reaction: For each Cr atom, a reduction of +3 oxidation states requires 3 electrons:
    

\[Cr^{6+} + 3e^- \rightarrow Cr^{3+}\]

1. Total Electrons for Two Cr Atoms: Since there are two Cr atoms in \(Cr_{2}O_{7}^{2-}\), the total number of electrons needed is:
    

\[2 \times 3 = 6 \text{ electrons}\]

Thus, the reduction of \(Cr_{2}O_{7}^{2-}\) to \(Cr^{3+}\) requires six electrons.