Question

Which of the following allotropes of silicon burns (oxidizes) in the air?
A. Amorphous silicon.
B. Crystalline silicon.
C. Both A and B.
D. None of the above.

Answer 1

Hint: We should note that there are two allotropes of silicone to answer this question: amorphous and crystalline. Amorphous silicon is a gray powder. Because some of the atoms are not fully bonded the structure is flexible. Crystalline silica is in nature greyish and shiny.

Complete step-by-step answer:
Allotropy or allotropism is the ability of certain chemical elements to occur in two or more different forms, in the same physical state, known as elemental allotropes. Allotropes are various structural modifications of an element, the element's atoms are bonded together in a different way.
There are two silicone allotropes:
1. Crystalline silicon.
2. Amorphous silicon.
Crystalline silicon (also called polycrystalline) is a metallic grey solid substance. The presence looks like small crystals. Since the atoms in the structure are fully bound, crystalline silicon is stronger and more stable than amorphous silicon. Crystalline silicon is used in solar cells, as is amorphous silicon. This is also used in electronic microchips, such as computers or smartphones
Amorphous silicon is a colour-brown powdery material. The atoms are mostly connected throughout the structure, but some atoms are not bonded to their maximum capacity. This makes silicon amorphous flexible but not particularly strong. Since silicon is a semiconductor (a substance capable of acting both as an electric conductor and an insulator), amorphous silicon is a great material for use in solar panels. Amorphous silicon is used particularly for solar cells used in calculators, watches, and more.
Amorphous silicon, in which certain atoms in the structure remain unbonded, lacks long-range order, but can in theory be manufactured much cheaper than multicrystalline silicon. Such a lack of long-range order in the structural arrangement of the atoms is the product of what is called "unsatisfied" bonds. To produce silica \[Si{O_2}\], this isotope burns in the air.
Therefore, we can say amorphous silicon is burning in the air to create silica.
So choice (A) is the right answer.

Note: First we need to know about allotropes when answering this problem and then we need to find out the silicon allotropes. After that we can easily find that it oxidizes at the surface level and catches fire when amorphous silicon is heated in air. Silicon burns brightly in the air to form silicon dioxide and fiercely in oxygen. It is an exothermic reaction: $Si + {O_2} \to Si{O_2}$.