Select the correct statements:

Options

A. pH of `NaHCO_3` solution can be given by `(pK_(H_2CO_3))+(pK_(HCO_3^(-)))/2`
B. `Al^(3+)` ion is amphoteric
C. `K_(SP)` values of metal nitrates are very-very high
D. `Na^+(aq)` is conjugate acid of NaOH(aq)

Explanation

To solve the question, we need to evaluate each of the four statements provided and determine whether they are correct or not.

### Step 1: Evaluate Statement 1
**Statement:** The pH of NaHCO3 solution can be given by pKH2CO3 + pKHCO3 divided by 2.

**Analysis:**
- NaHCO3 (sodium bicarbonate) is an amphiprotic substance, meaning it can act as both an acid and a base.
- The pH of a solution of an amphiprotic substance can be calculated using the average of the pKa values of its acidic and basic forms.
- Here, HCO3- is formed from H2CO3 by removing one proton. Thus, the pH can be expressed as:
\[ \text{pH} = \frac{\text{pKa}_1 + \text{pKa}_2}{2} \]
- Therefore, this statement is **correct**.

### Step 2: Evaluate Statement 2
**Statement:** Al3+ ion is amphoteric.

**Analysis:**
- Amphoteric substances can act as both acids and bases.
- Al3+ can react with bases to form complexes (like NaAl(OH)4) and can also react with acids to form Al(OH)3 and release protons.
- Since Al3+ can behave as both an acid and a base, this statement is **correct**.

### Step 3: Evaluate Statement 3
**Statement:** Ksp values of metal nitrates are very very high.

**Analysis:**
- Metal nitrates tend to have high solubility in water due to the high enthalpy of hydration (which is an exothermic process).
- This results in high Ksp values for metal nitrates, indicating they are soluble.
- Therefore, this statement is **correct**.

### Step 4: Evaluate Statement 4
**Statement:** Na+ aqueous is the conjugate acid of sodium hydroxide aqueous.

**Analysis:**
- When sodium hydroxide (NaOH) dissolves in water, it dissociates into Na+ and OH- ions.
- The OH- ion is the basic part, and Na+ can be considered as the conjugate acid of NaOH since it is formed when NaOH donates a hydroxide ion.
- Therefore, this statement is **correct**.

### Conclusion
All four statements are correct.

**Final Answer:** All statements (1, 2, 3, and 4) are correct.

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