Metal which is used in packaging and has a valency of $ + 3$ is:
A: Aluminum
B: Copper
C: Lead
D: Potassium
E: Iron
F: Silver

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Hint: Fundamental characteristics that metal should possess for packaging are compactness, high density, toughness, malleability, and high thermal resistance. Metals which will possess these properties can be used for packaging.

Complete step by step answer:
In this question, we have to find metal that is used in packaging and has a valency of $ + 3$. So let’s find out the metals which have $ + 3$ valency among given options. The atomic number of aluminum is $13$. It has $3$ electrons in its valence shell. So its valency is $ + 3$. Valency is defined as the number of electrons that an atom will lose or gain in order to achieve noble gas (inert gas) configuration. If an atom gains electron valency is negative and if it loses electron valency is positive. Aluminum has a valency of $ + 3$ so it could be the answer but let’s check other options first. Copper shows valency of $ + 1$ and $ + 2$ but we need $ + 3$ valency so it is not the answer. Lead shows valency of $ + 4$ and $ + 2$ this means this is also not the answer. Potassium has a valency of $ + 1$ so it is not the answer. Iron exhibits two oxidation states $ + 2$ and $ + 3$. So it could be the answer. Silver also shows a $ + 3$ oxidation state but being expensive it could not be used for packaging. Now the correct answer is either aluminum or iron. Iron reacts with oxygen and moisture to form rust. So it is not suitable for high-moisture food contact.

So, the correct answer is aluminum that is option A.

Nitrogen being inert gas (it does not react with foodstuff) is used in packaging. It keeps foodstuff fresh and protects the nutrients. Nitrogen provides a pressurized atmosphere to food packages that prevent package collapse.