`FeCr_(2)O_(4)+NaOH+"air" to (A)+Fe_(2)O_(3)`
`(A)+(B) to Na_(2)Cr_(2)O_(7)`
`Na_(2)Cr_(2)O_(7)+X overset(Delta)to Cr_(2)O_(3)`
`Cr_(2)O_(3)+Y overset(Delta)to Cr`
Compound (A) and (B) are :

Options

A. `Na_(2)CrO_(4), H_(2)SO_(4)`
B. `Na_(2)Cr_(2)O_(7),HCl`
C. `Na_(2)CrO_(5), H_(2)SO_(4)`
D. `Na_(4)[Fe(OH)_(6)], H_(2)SO_(4)`

Answer

To solve the given problem step by step, we will analyze the reactions provided and identify the compounds (A) and (B).

### Step 1: Identify the first reaction
The first reaction given is:
\[ \text{FeCr}_2\text{O}_4 + \text{NaOH} + \text{air} \rightarrow (A) + \text{Fe}_2\text{O}_3 \]

In this reaction, iron chromite (\(\text{FeCr}_2\text{O}_4\)) reacts with sodium hydroxide (\(\text{NaOH}\)) and oxygen (from air) to produce sodium chromate (\(\text{Na}_2\text{CrO}_4\)) and iron(III) oxide (\(\text{Fe}_2\text{O}_3\)).

The balanced equation for this reaction is:
\[ \text{FeCr}_2\text{O}_4 + 4 \text{NaOH} + \text{O}_2 \rightarrow 2 \text{Na}_2\text{CrO}_4 + \text{Fe}_2\text{O}_3 + 2 \text{H}_2\text{O} \]

Thus, compound (A) is:
\[ (A) = \text{Na}_2\text{CrO}_4 \]

### Step 2: Identify the second reaction
The second reaction is:
\[ (A) + (B) \rightarrow \text{Na}_2\text{Cr}_2\text{O}_7 \]

From the previous step, we know that (A) is \(\text{Na}_2\text{CrO}_4\). To convert sodium chromate to sodium dichromate (\(\text{Na}_2\text{Cr}_2\text{O}_7\)), we need to react it with sulfuric acid (\(\text{H}_2\text{SO}_4\)).

The balanced equation for this reaction is:
\[ 2 \text{Na}_2\text{CrO}_4 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{Cr}_2\text{O}_7 + \text{Na}_2\text{SO}_4 + \text{H}_2\text{O} \]

Thus, compound (B) is:
\[ (B) = \text{H}_2\text{SO}_4 \]

### Step 3: Identify the third reaction
The third reaction is:
\[ \text{Na}_2\text{Cr}_2\text{O}_7 + X \overset{\Delta}{\rightarrow} \text{Cr}_2\text{O}_3 \]

Sodium dichromate can be reduced to chromium(III) oxide (\(\text{Cr}_2\text{O}_3\)) using a reducing agent. A common reducing agent for this reaction can be carbon (C) or zinc (Zn).

The balanced equation for this reaction can be:
\[ \text{Na}_2\text{Cr}_2\text{O}_7 + 3 \text{C} \rightarrow \text{Cr}_2\text{O}_3 + 2 \text{Na}_2\text{CO}_3 \]

### Step 4: Identify the fourth reaction
The fourth reaction is:
\[ \text{Cr}_2\text{O}_3 + Y \overset{\Delta}{\rightarrow} \text{Cr} \]

To convert chromium(III) oxide to chromium metal, we can use aluminum (Al) as a reducing agent. This is a thermite reaction.

The balanced equation for this reaction is:
\[ 2 \text{Cr}_2\text{O}_3 + 3 \text{Al} \rightarrow 4 \text{Cr} + 3 \text{Al}_2\text{O}_3 \]

### Final Answer
Thus, the compounds (A) and (B) are:
- \( (A) = \text{Na}_2\text{CrO}_4 \)
- \( (B) = \text{H}_2\text{SO}_4 \)