**Core Concept**
Invert sugar is a type of disaccharide composed of glucose and fructose molecules bonded together. This sugar is formed when sucrose (table sugar) is hydrolyzed, resulting in an equimolar mixture of glucose and fructose.

**Why the Correct Answer is Right**
Invert sugar is formed through the inversion of sucrose, a process that occurs when the alpha-glycosidic bond between glucose and fructose is broken. This reaction is catalyzed by the enzyme sucrase in the small intestine, but can also be achieved through acid hydrolysis. The resulting mixture of glucose and fructose has a different physical and chemical properties compared to sucrose, such as a lower melting point and a sweeter taste.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the composition of invert sugar.
**Option B:** This option is incorrect because it suggests that invert sugar is a simple sugar, whereas it is actually a disaccharide composed of glucose and fructose.
**Option C:** This option is incorrect because it does not accurately describe the process of forming invert sugar.

**Clinical Pearl / High-Yield Fact**
Invert sugar is commonly used in food products and pharmaceuticals due to its unique properties, such as its ability to dissolve easily in water and its sweet taste. It is also used as a sweetener in some medical applications, such as in the treatment of certain gastrointestinal disorders.

**Correct Answer:** D.