To determine which of the statements is not correct, we will analyze each statement one by one.
### Step 1: Analyze the First Statement
**Statement:** All metal carbonates react with acid to give salt, water, and carbon dioxide.
**Analysis:** This statement is correct. When metal carbonates react with acids, they produce a salt, water, and carbon dioxide gas. For example, when calcium carbonate (CaCO₃) reacts with hydrochloric acid (HCl), it produces calcium chloride (CaCl₂), water (H₂O), and carbon dioxide (CO₂).
### Step 2: Analyze the Second Statement
**Statement:** All metal oxides react with water to give salt and acid.
**Analysis:** This statement is incorrect. Most metal oxides are insoluble in water. Only a few metal oxides, like sodium oxide (Na₂O) and calcium oxide (CaO), react with water to form hydroxides (NaOH and Ca(OH)₂, respectively). Therefore, the majority of metal oxides do not react with water.
### Step 3: Analyze the Third Statement
**Statement:** Some metals react with acids to give salt and hydrogen.
**Analysis:** This statement is correct. Certain metals, such as sodium (Na) and magnesium (Mg), react with acids to produce a salt and hydrogen gas. For instance, sodium reacts with hydrochloric acid to form sodium chloride (NaCl) and hydrogen gas (H₂).
### Step 4: Analyze the Fourth Statement
**Statement:** Some non-metal oxides react with water to form an acid.
**Analysis:** This statement is correct. Non-metal oxides, such as sulfur dioxide (SO₂) and carbon dioxide (CO₂), can react with water to form acids (like sulfurous acid and carbonic acid, respectively). Thus, this statement holds true.
### Conclusion
After analyzing all the statements, we find that the second statement is the one that is not correct.
**Final Answer:** The statement that is not correct is: "All metal oxides react with water to give salt and acid."
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