Which non-metal sublime on heating and have metallic lusture.

Explanation

To solve the question "Which non-metal sublime on heating and have metallic luster?", we can follow these steps:

### Step 1: Identify the properties of non-metals
Non-metals are elements that typically lack metallic properties. They are generally poor conductors of heat and electricity, and they tend to gain electrons during chemical reactions. However, some non-metals can exhibit unique properties under certain conditions.

**Hint:** Remember that non-metals usually do not have metallic luster, but some exceptions exist.

### Step 2: Understand the process of sublimation
Sublimation is the process where a solid turns directly into a gas without passing through the liquid state. This occurs under specific conditions, typically involving a change in temperature and pressure.

**Hint:** Think about common substances that sublime when heated.

### Step 3: Explore the halogens
The halogens are a group of non-metals in Group 17 of the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Among these, iodine is known for its ability to sublime when heated.

**Hint:** Recall the order of halogens and their physical states at room temperature.

### Step 4: Analyze iodine's characteristics
Iodine is a solid at room temperature and has a deep purple color. When heated, it sublimates to form a violet gas. Iodine is unique among non-metals because it can exhibit a metallic luster due to the emission of energy when its electrons return to lower energy states.

**Hint:** Consider why iodine might display metallic luster despite being a non-metal.

### Step 5: Conclude the answer
Based on the properties of non-metals, the process of sublimation, and the characteristics of iodine, we can conclude that the non-metal that sublimes on heating and has metallic luster is **iodine**.

**Final Answer:** Iodine.