What is the oxidation number of the underlined atoms in the following :
(a) `Na_(2)Cr_(2)O_(7)`
(b) `Na_(3)PO_(4)`

Explanation

To determine the oxidation numbers of the specified atoms in the compounds \( \text{Na}_2\text{Cr}_2\text{O}_7 \) and \( \text{Na}_3\text{PO}_4 \), we can follow these steps:

### (a) Finding the oxidation number of Chromium (Cr) in \( \text{Na}_2\text{Cr}_2\text{O}_7 \):

1. **Identify the oxidation states of the other elements**:
- Sodium (Na) has an oxidation state of \( +1 \).
- Oxygen (O) has an oxidation state of \( -2 \).

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