Misch metal is a well-known alloy consisting of a lanthanoid metal (around $95\%$, predominantly cerium and lanthanum), iron (about $5\%$), and traces of sulfur, carbon, calcium, and aluminum. Magnesium-based alloys with misch metal are pyrophoric and used in making bullets, shells, and lighter flints.

Comparison of test results:

• 2,4-DNP test is given by all aldehydes and ketones, so both give positive tests.
• Tollens' test is reduced by both aliphatic aldehydes (acetaldehyde) and aromatic aldehydes (benzaldehyde) to form a silver mirror.
• Sodium bicarbonate test is used to detect carboxylic acids, neither aldehyde gives effervescence.
• Fehling's test: Aliphatic aldehydes like acetaldehyde reduce Fehling's solution to give a red precipitate of cuprous oxide ($\text{Cu}_2\text{O}$), whereas aromatic aldehydes like benzaldehyde do not reduce Fehling's solution.

In the MacArthur-Forrest cyanide process for silver extraction:

• Leaching (Oxidation): The crushed silver ore is treated with a dilute solution of $\text{NaCN}$ in the presence of atmospheric oxygen ($\text{O}_2$), which acts as the oxidising agent:
  $$4\text{Ag} + 8\text{CN}^- + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 4[\text{Ag}(\text{CN})_2]^- + 4\text{OH}^-$$
• Precipitation (Reduction): Zinc dust is added to reduce the dicyanoargentate(I) complex to metallic silver, where $\text{Zn}$ acts as the reducing agent:
  $$2[\text{Ag}(\text{CN})_2]^- + \text{Zn} \rightarrow [\text{Zn}(\text{CN})_4]^{2-} + 2\text{Ag}$$