Four solids W,X , Y and Z are given . All have a metallic lustre. The solids could be gold, lead sulphide , mica (which is quartz or `SiO_2`) and iodine . The results of the investigation are :
(a)W is a good electrical conductor . X,Y and Z are poor electrical conductors
(b)When the solids are hit with a hammer, W flattens out , X shaltters into many pieces, Y is smashed into a powder and Z is not affected .
(c )When the solids are heated with a Bunsen burner, Y melts with some sublimation, but X, W and Z do not melt.
(d)In treatment with `7M HNO_3`, X dissolves and there is no effect on W,Y or Z
On the basis of these test results, identify the solids

Explanation

To identify the solids W, X, Y, and Z based on the given information, we can analyze each clue step by step.

### Step 1: Identify W
- **Given Information**: W is a good electrical conductor.
- **Analysis**: Among the options (gold, lead sulfide, mica, iodine), gold is known to be an excellent conductor of electricity.
- **Conclusion**: W is **gold**.

### Step 2: Analyze X, Y, and Z
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