If two substances react to form one product , a reaction has occurred

a - double displacement
b - single displacement
c - combustion
d - synthesis

If two substances react to form one product , a synthesis reaction has occurred

Explanation:

The reaction in which multiple substances react to form a single product then it is called a synthesis reaction.

The synthesis reaction in general form is given by:

where maybe any compound or elements and is the compound product formed by the reactants.

An example of this form of reaction is:

Formation of water

Here 2 moles of hydrogen reacts with 1 mole of oxygen to give 2 moles of water.

d is the correct answer

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.