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Q83 (NDA-II/2012) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles Answer Verified

Which one among the following is the correct order of strenght of acids?

Result
Your answer: —  Â·  Correct: A
Explanation

The strength of an acid is determined by its ability to dissociate and produce hydrogen ions (H+) in solution [1]. Sulfuric acid (H2SO4) is classified as a strong mineral acid because its first dissociation is essentially complete, with a very high Ka value. Phosphorous acid (H3PO3), while not explicitly listed in all tables, is a moderately weak diprotic acid; however, it is significantly stronger than acetic acid (CH3COOH). Acetic acid is a well-known weak organic acid with a pKa of approximately 4.76, indicating very little dissociation in aqueous solution [1]. Therefore, the correct order of decreasing acid strength is H2SO4 (strongest) > H3PO3 (moderate/weak) > CH3COOH (weakest). This sequence aligns with the general principle that mineral acids are typically stronger than organic carboxylic acids [1].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? > p. 26
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