Question

which of these formulas is written incorrectly?
a) ca(oh)₂
b) al₂(so₄)₃
c) (nh₄)₂s
d) aloh₃

Explanation:

Step1: Analyze the charge balance

For ionic compounds, the sum of positive and negative charges should be zero.

• For \(Ca(OH)_2\): \(Ca^{2 +}\) and \(2OH^{-}\), \(2+( - 2)=0\).
• For \(Al_2(SO_4)_3\): \(2Al^{3 +}\) (\(2\times3 = 6\) positive charges) and \(3SO_4^{2 -}\) (\(3\times(- 2)=-6\) negative charges), \(6+( - 6)=0\).
• For \((NH_4)_2S\): \(2NH_4^{+}\) (\(2\times1 = 2\) positive charges) and \(S^{2 -}\) (\(-2\) negative charge), \(2+( - 2)=0\).
• For \(AlOH_3\): \(Al^{3 +}\) and \(3OH^{-}\), but the correct formula should be \(Al(OH)_3\) to show the poly - atomic ion \(OH^{-}\) clearly.

Answer:

D. \(AlOH_3\)