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Hi there.
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In this question, we have three almost puzzle -like questions that are asking us to write the formula for some compounds.
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So i pulled in the periodic table because that's going to be very helpful.
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So in letter a, we have an ionic compound whose cat ion is a transition metal with 25 protons.
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So we are looking for atomic number 25, which is mn, because 20.
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25 protons tells us the atomic number.
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So it's mn, but it only has 22 electrons.
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So it has three fewer electrons.
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So that means you would have a three plus charge.
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And we're combining that with an anion, who is an oxoanion, oxyanion.
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That means it's oxygen with nitrogen.
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So it's a polyatomic ion composed of nitrogen and two oxygen atoms.
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That would be the nitrite ion.
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And it has a one negative charge.
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So that means to make the charges add to zero, we need to have three of those nitrite ions.
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So it is going to be mn, no2, 3.
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And for my final formula, i can go ahead and remove the charges.
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Okay, let's go on to letter b then.
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In letter b, we have a metalloid in group 13.
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This periodic table is not numbered, but group 13 is right there.
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And metalloids lie along a staircase line that starts between boron and aluminum.
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However, aluminum is considered a pure metal.
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It is not a metaloid.
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So boron is the only metaloid in group 13 and three atoms of a halogen in period 2...