Among the following, the number of underlined elements having `+5` oxidation state are
`ul(Fe)_(3)O_(4),K_(2)ul(Cr)_(2)O_(7),Hul(Cl)O_(3),ulP_(2)O_(7)^(4-),ulSO_(4)^(2-)`

Explanation

To determine the number of underlined elements with a +5 oxidation state from the given compounds, we will analyze each compound one by one.

### Step 1: Analyze Fe₃O₄
1. **Identify the oxidation states**:
- Let the oxidation state of Fe be \( x \).
- There are 3 Fe atoms and 4 O atoms (with O having an oxidation state of -2).
- The equation for the overall charge (which is 0) is:
\[ 3x + 4(-2) = 0 \]
- Simplifying gives:
\[ 3x - 8 = 0 \implies 3x = 8 \implies x = \frac{8}{3} \]
- The oxidation state of Fe is \( \frac{8}{3} \), which is not +5.

### Step 2: Analyze K₂Cr₂O₇
2. **Identify the oxidation states**:
- Let the oxidation state of Cr be \( x \).
- Potassium (K) has an oxidation state of +1.
- The equation for the overall charge (which is 0) is:
\[ 2(+1) + 2x + 7(-2) = 0 \]
- Simplifying gives:
\[ 2 + 2x - 14 = 0 \implies 2x - 12 = 0 \implies 2x = 12 \implies x = 6 \]
- The oxidation state of Cr is +6, which is not +5.

### Step 3: Analyze HClO₃
3. **Identify the oxidation states**:
- Let the oxidation state of Cl be \( x \).
- The equation for the overall charge (which is 0) is:
\[ 1 + x + 3(-2) = 0 \]
- Simplifying gives:
\[ 1 + x - 6 = 0 \implies x - 5 = 0 \implies x = 5 \]
- The oxidation state of Cl is +5.

### Step 4: Analyze P₂O₇⁴⁻
4. **Identify the oxidation states**:
- Let the oxidation state of P be \( x \).
- The equation for the overall charge (which is -4) is:
\[ 2x + 7(-2) = -4 \]
- Simplifying gives:
\[ 2x - 14 = -4 \implies 2x = 10 \implies x = 5 \]
- The oxidation state of P is +5.

### Step 5: Analyze SO₄²⁻
5. **Identify the oxidation states**:
- Let the oxidation state of S be \( x \).
- The equation for the overall charge (which is -2) is:
\[ x + 4(-2) = -2 \]
- Simplifying gives:
\[ x - 8 = -2 \implies x = 6 \]
- The oxidation state of S is +6, which is not +5.

### Conclusion
From the analysis, we find that the elements with a +5 oxidation state are:
- Cl in HClO₃
- P in P₂O₇⁴⁻

Thus, the number of underlined elements having a +5 oxidation state is **2**.

---