The first one I god it wrong and he told us the answer
Answer:
One of each
Explanation:
Be is in Group 2, so it loses its two valence electrons in a reaction to form Be²⁺ ions.
Carbonate ion has the formula CO₃²⁻.
We can use the criss-cross method to work out the formula of beryllium carbonate.
The steps are
Write the symbols of the anion and cation.
Criss-cross the numbers of the charges to become the subscripts of the other ion.
Write the formula with the new subscripts.
Divide the subscripts by their highest common factor.
Omit all subscripts that are 1.
When you use this method with Be²⁺ and CO₃²⁻, you might be tempted to write the formula for the beryllium carbonate as Be₂(CO₃)₂
However, you can divide the subscripts by their largest common factor (2).
This gives you the formula Be₁(CO₃)₁.
We omit subscripts that are 1, so the correct formula is
BeCO₃
There is one Be²⁺ ion and one CO₃²⁻ ion in a formula unit of beryllium carbonate.
The red sign pops up on the side of the bus.

The Correct choices are :
- 1. The elements have filled valence levels.
- 2. potassium (K) with a 1+ charge
You must remember that oxidation number of hydrogen in acids is always +1, oxidation number of oxygen in oxides & acids is always -2... metals has always oxidation number on plus!
group NO3 comes from HNO3...and oxidation number of whole acid group is always on minus and equal to the amount of hydrogen atoms in this acid... so oxidation number of NO3 = -1
we have 2 NO3 groups so 2*(-1) = -2 and that is the reason why oxidation number of Fe in this formula must be +2... because sum of all elements always gives 0!
Now we could count of oxidation number for nitrogen... we write HNO3 and start counting from right to left:
3*(-2) from oxygens + 1 from hydrogen = -5
so nitrogen must have +5 oxidation number... because sum all in formula must be 0.