Which of the following statements about the diels-alder reaction are true?
a. it is a reaction involving pi-electrons.
b. it is a [1+3] cycloaddition.
c. it is a stepwise reaction.
d. it is *not* a reaction favored by entropy considerations.
e. it is a photochemical reaction.

A.It is a reaction involving pi-electrons.

D.It is *not* a reaction favored by entropy considerations.

Explanation:

The Diels-Alder reaction is a [4+2]- cycloadition that involoves pi-electrons (4 from the diene and 2 from the dienophile).

The reaction is favored by the formation of new sigma bond, since they are more stable than pi-bonds. This reaction is not favored by entropy because there are 2 reactants and one product and the order increases.

The reaction happens in one step.

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).