Question

Assertion: The order of densities of the various allotropes of phosphorus is as follows: Black phosphorus, red phosphorus, white phosphorus
Reason: As the tendency of polymerization increases, the compactness of substances also increases.
$A)$ Assertion is incorrect and reason is correct.
$B)$ Both assertion and reason are correct but reason is not the correct explanation for assertion.
$C)$ Assertion is correct and reason is incorrect.
$D)$ Both assertion and reason are correct and reason is the correct explanation for the assertion.

Answer 1

Allotropy is the property of some substance components to exist in at least two distinct structures, in a similar actual state, known as allotropes of the components.

Complete answer:
Because the order of densities of phosphorus allotropes is black phosphorus> red phosphorus> white phosphorus. The change between allotropic structures is set off by the very forces that influence different reactions, i.e., pressure, light, and temperature.
And in polymerization the number of monomers are being bound together in a macromolecule, the quantity of levels of degree of freedom is continually decreasing. Therefore, the tendency of polymerization increases, the compactness of the substance also increases.
Correct answer is $D)$ .

Additional Information:
Let’s know more about each phosphorus allotropes
White allotrope- White phosphorus exists as particles composed of four ions in a tetrahedral structure. The tetrahedral arrangement plan brings about instability. The particle is portrayed as consisting of six single P–P bonds.
Red allotrope- Red phosphorus might be framed by white phosphorus without air or by presenting white phosphorus to daylight. Red phosphorus exists as amorphous. Upon additional warming, the shapeless red phosphorus solidifies.
Black allotrope- It is the thermodynamically steady type of phosphorus at room temperature and pressure.

Note:
White phosphorus allotrope is the most reactive, least steady and generally harmful of the three. It comprises four phosphorus atoms that synthetically cling to frame a tetrahedral shape.