Question at position 2 Which series is the correct order of decreasing acid strength for each group of acids? (Strongest acid weakest acid) HClO4 HClO3 HClO2 HClO HClO3 HClO4 H2SO4 HNO3 HF HCl HBr HI H2S H2Te H2Se H2O

Question

Question at position 2 Which series is the correct order of decreasing acid strength for each group of acids? (Strongest acid > > > weakest acid) HClO4 > HClO3 > HClO2 > HClO HClO3 > HClO4 > H2SO4 > HNO3 HF > HCl > HBr > HI H2S > H2Te > H2Se > H2O单项选择题

A

HClO4 > HClO3 > HClO2 > HClO

B

HClO3 > HClO4 > H2SO4 > HNO3

C

HF > HCl > HBr > HI

D

H2S > H2Te > H2Se > H2O

BlackTom AI · Accepted Answer

Oxyacid acidity increases with the number of oxygen atoms bonded to the central atom because additional oxygens withdraw electron density (inductive effect) and allow greater resonance stabilization of the conjugate base, making proton loss easier.

1) Relevant concepts
- Oxyacid strength correlates with (a) number of oxygen atoms attached to the central atom and (b) oxidation state of the central atom. More O atoms → stronger −I effect and more resonance structures for the conjugate base → greater stabilization → larger Ka (stronger acid).
- Conjugate base resonance and inductive effects determine acidity for oxyacids; for binary hydrogen halides and hydrides other trends (bond strength, H–X bond polarity, and atomic size) apply.

2) Step-by-step reasoning
- Compare HClO4, HClO3, HClO2, HClO:
  Step A: Count oxygens and likely resonance in conjugate bases:
    ClO4−: 4 oxygen atoms → 4 resonance-equivalent O atoms (charge delocalized over 4 O).
    ClO3−: 3 oxygens → 3 resonance forms.
    ClO2−: 2 oxygens → 2 resonance forms.
    ClO−: 1 oxygen → minimal resonance.
  Step B: Calculate oxidation states of Cl (intermediate steps):
    For HClO4: H(+1) + Cl(x) + 4·O(−2) = 0 → +1 + x −8 = 0 → x = +7.
    HClO3: +1 + x −6 = 0 → x = +5.
    HClO2: +1 + x −4 = 0 → x = +3.
    HClO:  +1 + x −2 = 0 → x = +1.
  Step C: Higher Cl oxidation state and more oxygens mean stronger electron withdrawal and better stabilization of the anion → stronger acid.

3) Intermediate calculations shown above (oxidation states and resonance counts).

4) Why the correct answer is correct
HClO4 (perchloric acid) is strongest because Cl is at +7 and ClO4− is highly resonance-stabilized; progressively fewer O atoms and lower Cl oxidation states reduce stabilization and acidity, giving the order HClO4 > HClO3 > HClO2 > HClO.

5) Why the other options are incorrect (brief)
- "HClO3 > HClO4 > H2SO4 > HNO3": places HClO3 above HClO4 (wrong) and mixes unrelated acids without correct ordering.
- "HF > HCl > HBr > HI": reversed for hydrogen halides; acidity actually increases down the group (HI strongest, HF weakest) due to bond strength/size.
- "H2S > H2Te > H2Se > H2O": incorrect order for hydrides of Group 16; acidity increases down the group: H2Te > H2Se > H2S > H2O.

6) Conclusion
All reasoning above confirms the correct decreasing acid strength order is HClO4 > HClO3 > HClO2 > HClO, matching the provided answer.

Question at position 2 Which series is the correct order of decreasing acid strength for each group of acids? (Strongest acid > > > weakest acid) HClO4 > HClO3 > HClO2 > HClO HClO3 > HClO4 > H2SO4 > HNO3 HF > HCl > HBr > HI H2S > H2Te > H2Se > H2O单项选择题

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