Choose the correct code by identifying (X), (Y) and (Z) in each case for the changes indicated:
(i) `CrO_(2)Cl_(2) overset(KOH) to (X) overset(conc." "H_(2)SO_(4))to(Y) overset(AgNO_(3))to(Z)`
(ii) `CrCl_(3)(aq) underset(NaOH)overset("excess")to (X) underset(H_(2)O," boil")overset(Na_(2)O_(2))to (Y) underset("acetate")overset("lead")to (Z)`
(iii) `ZnSO_(4)(aq) overset(Na_(2)CO_(3))to (X) overset(Delta)to (Y) underset("nitrate, "Delta)overset("cobalt")to(Z)`
(iv) `CuCl_(2)(aq) underset(H_(2)S)overset(NH_(4)OH)to (X) underset(Delta)overset(HNO_(3))to (Y) underset("excess")overset(KCN)to(Z)`

Options

A. `X=K_(2)CrO_(4)" "Y=K_(2)Cr_(2)O_(7)" "Z=Ag_(2)CrO_(4)`
B. `X=[Cr(OH)_(4)]^(-) " "Y=Na_(2)CrO_(4)" "Z=PbCrO_(4)`
C. `X=ZnCO_(3)" "Y=ZnO" "Z=CoZnO_(2)`
D. `X=CuS" "Y=Cu(NO_(3))_(2)" "Z=K_(3)[Cu(CN)_(4)]`

Answer

To solve the given question, we will analyze each reaction step by step to identify the compounds (X), (Y), and (Z).

### (i) Reaction: `CrO2Cl2 + KOH → (X) → (Y) → (Z)`

1. **Step 1:** When `CrO2Cl2` is treated with `KOH`, it forms `K2CrO4`.
- **Identified as (X):** K2CrO4

2. **Step 2:** When `K2CrO4` is treated with concentrated `H2SO4`, it forms `K2Cr2O7`.
- **Identified as (Y):** K2Cr2O7

3. **Step 3:** When `K2Cr2O7` is treated with `AgNO3`, it forms `Ag2Cr2O7`.
- **Identified as (Z):** Ag2Cr2O7

### (ii) Reaction: `CrCl3(aq) + NaOH(excess) → (X) → (Y) → (Z)`

1. **Step 1:** When `CrCl3` in aqueous solution is treated with excess `NaOH`, it forms `NaCr(OH)4`.
- **Identified as (X):** NaCr(OH)4

2. **Step 2:** When `NaCr(OH)4` is boiled with water, it forms `Na2CrO4`.
- **Identified as (Y):** Na2CrO4

3. **Step 3:** When `Na2CrO4` is treated with lead acetate, it does not form a precipitate in basic medium.
- **Identified as (Z):** No precipitate (not a specific compound)

### (iii) Reaction: `ZnSO4(aq) + Na2CO3 → (X) → (Y) → (Z)`

1. **Step 1:** When `ZnSO4` in aqueous solution reacts with `Na2CO3`, it forms `ZnCO3·3Zn(OH)2`.
- **Identified as (X):** ZnCO3·3Zn(OH)2

2. **Step 2:** When `ZnCO3·3Zn(OH)2` is boiled, it decomposes to form `ZnO`.
- **Identified as (Y):** ZnO

3. **Step 3:** When `ZnO` is treated with cobalt nitrate and heated, it forms `CoZnO2`.
- **Identified as (Z):** CoZnO2

### (iv) Reaction: `CuCl2(aq) + H2S → (X) → (Y) → (Z)`

1. **Step 1:** When `CuCl2` in aqueous solution is treated with `H2S`, it forms `CuS`.
- **Identified as (X):** CuS

2. **Step 2:** When `CuS` is treated with `HNO3` and heated, it forms `Cu(NO3)2`.
- **Identified as (Y):** Cu(NO3)2

3. **Step 3:** When `Cu(NO3)2` is treated with excess `KCN`, it forms `K3[Cu(CN)4]`.
- **Identified as (Z):** K3[Cu(CN)4]

### Summary of Identifications:
- (i) X = K2CrO4, Y = K2Cr2O7, Z = Ag2Cr2O7
- (ii) X = NaCr(OH)4, Y = Na2CrO4, Z = No precipitate
- (iii) X = ZnCO3·3Zn(OH)2, Y = ZnO, Z = CoZnO2
- (iv) X = CuS, Y = Cu(NO3)2, Z = K3[Cu(CN)4]

### Final Answer:
The correct code by identifying (X), (Y), and (Z) in each case for the changes indicated is:
- (i) K2CrO4, K2Cr2O7, Ag2Cr2O7
- (ii) NaCr(OH)4, Na2CrO4, No precipitate
- (iii) ZnCO3·3Zn(OH)2, ZnO, CoZnO2
- (iv) CuS, Cu(NO3)2, K3[Cu(CN)4]