The metal has began to rust changing its physical appearance.
Answer:

Explanation:
Hello,
In this case, considering that the compound is 48% oxygen, we infer it is 52% chromium, therefore, by using their atomic masses we compute the moles by assuming those percentages as masses:

Next, by dividing by the smallest moles, we find the subscripts in the empirical formula:

Which are also expressed in the smallest whole numbers, therefore the empirical formula is:

Which corresponds to the chromic oxide or chromium (IV) oxide.
Regards.
Explanation:
A and D. the answer is a and d
These percentages are most likely mass percentages. Therefore, determine the mass of each element in 100g of the compound.
<span>75g C, 25g H. </span>
<span>Divide these masses by their molar mass to find the ratios of the moles of element in the compound. Divide these values by the smallest of the two/three to get the ratios. </span>
<span>6.25:25 C:H --> 1:4 </span>
<span>So the formulae are CH4 (methane).</span>