For a given alkyl group the densities of the halides follow the order

Options

A. RI`lt ` RBr `lt` RCl
B. RI `lt` RCl `lt` RBr
C. RBr `lt` RI `lt` RCl
D. RCl `lt` RBr `lt` RI

Answer

To determine the order of densities of haloalkanes (halides) for a given alkyl group, we can analyze the relationship between the size and mass of the halogen atoms involved. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Halogens
The halogens we are considering are fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

### Step 2: Understand the Trend in Atomic Size
As we move down the group in the periodic table from fluorine to iodine, the atomic size increases. This is due to the addition of electron shells, which increases the distance of the outer electrons from the nucleus.

### Step 3: Relate Size to Mass
With the increase in atomic size, there is also an increase in atomic mass. Heavier atoms will contribute to a higher density when they are part of a compound, such as haloalkanes.

### Step 4: Determine the Density Order
Since density is proportional to mass (assuming volume remains relatively constant), we can conclude that:
- Iodine (I) has the highest mass and thus will have the highest density.
- Bromine (Br) has a lower mass than iodine but higher than chlorine.
- Chlorine (Cl) has a lower mass than bromine but higher than fluorine.
- Fluorine (F) has the lowest mass and thus the lowest density.

Thus, the order of densities for the haloalkanes with a common alkyl group (R) is:
\[ R-I > R-Br > R-Cl > R-F \]

### Step 5: Final Conclusion
The correct order of densities for the halides is:
\[ R-I > R-Br > R-Cl > R-F \]