The chart shows the process of extraction of some metals.

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Which of these metals requires electricity for extraction from its ore?

The table shows four different materials and their resistivity.

How many atoms of sulphur will react with one atom of magnesium to form a compound? 

Listed here is the reactivity of certain metals:

From the list above, identify the metal(s) that are likely to be found in a pure state in the Earth's Crust.

The blue-coloured solution of the sulphate salt of metal $\mathrm{W}$ is taken in a beaker. Metal powders $\mathrm{X}, \mathrm{Y}$ and $Z$ are added one after the other to the beaker. The colour changes occurring in the solution are shown below:

$\underset{\mathrm{blue} \mathrm{solution}}{\mathrm{W}-{\mathrm{SO}}_4}\stackrel{\mathrm{Metal} \mathrm{X}}{\to }\mathrm{colourless} \mathrm{solution}\stackrel{\mathrm{Metal} \mathrm{Y}}{\to }\mathrm{Pink} \mathrm{solution}\stackrel{\mathrm{Metal} \mathrm{Z}}{\to }\mathrm{Green} \mathrm{solution}$

State what colour change, if any, will occur if metal $\mathrm{X}$ is again added to the green solution in the beaker. Explain Why. 

A piece of iron rusts when it comes in contact with air and moisture. Prakash had two identical shiny iron pieces $\mathrm{P}$ and $\mathrm{Q}$. To prevent the pieces from rusting, he coated piece $\mathrm{P}$ with oil paint and he galvanised piece $\mathrm{Q}$ with a coat of zinc metal. He noticed that the coatings were not complete and that a small part of the iron was exposed in both the pieces.

What is Prakash likely to observe about the exposed parts of the two iron pieces after some days? Explain why.