Metal Carbonyl

Step 1: Understanding CO stretching frequency.
The CO stretching frequency is influenced by the electron density on the metal. Higher electron density on the metal leads to a lower stretching frequency because the metal-carbon bond becomes weaker.
Step 2: Analyzing the options.
- (1) : Vanadium has a positive charge, which attracts electron density from the CO ligands, increasing the CO stretching frequency. - (2) : Cobalt in this complex is in a negative oxidation state, which increases electron density on the CO ligands, slightly decreasing the CO stretching frequency. - (3) : Nickel in this complex is neutral, and the electron density on the CO ligands is balanced, leading to a moderate CO stretching frequency. - (4) : Iron in this complex is in a negative oxidation state, which greatly increases electron density on the CO ligands, leading to the lowest CO stretching frequency.
Step 3: Conclusion.
The correct answer is (4) , as the increased electron density on the CO ligands lowers the CO stretching frequency.

Step 1: Alkali metals in liquid ammonia.
When alkali metals dissolve in liquid ammonia, they form blue solutions due to the presence of solvated electrons. The blue colour is a result of these solvated electrons being in an excited state. As the concentration of the alkali metal increases, the solution turns bronze due to the aggregation of solvated electrons.
Step 2: Paramagnetism and diamagnetism.
The blue solution is paramagnetic because of the unpaired solvated electrons, whereas the bronze solution becomes diamagnetic as the electrons pair up.
Step 3: Conclusion.
Therefore, all the facts given above are correct. The correct answer is (4) All the facts given above are correct.