Question

What is L and D glucose?

Answer 1

D-glucose: A carbon atom is connected to an oxygen and hydrogen atom in the glucose molecule. A double-bonded oxygen atom is found on the other end of the glucose molecule. The oxygen and hydrogen group at the top of the atom points to the right in the Fischer projection of D-glucose with the double-bonded oxygen atom pointed down.
D-glucose and L-glucose both have the same number of atoms. In Fischer projection, the oxygen and hydrogen group of atoms in L-glucose point to the left, unlike D-glucose. If these two molecules were to face each other, they would appear to be a mirror image of each other.

Complete answer:

L GLUCOSE	D GLUCOSE
Plane polarised light rotates in an anticlockwise direction.	Plane polarised light rotates in a clockwise direction.
One OH group in the Haworth projection of L glucose is pointing upward, whereas the other OH groups are pointing downward.	One OH group in the Haworth projection of D glucose is pointing downward, while the other OH groups are pointing upward.
One OH group is on the right side of the main carbon chain in the Fischer projection of L glucose, while the other OH groups are on the left side.	One OH group is on the left side of the main carbon chain in the Fischer projection of D glucose, while the other OH groups are on the right side.
The sugar molecule is in short supply.	The molecule of sugar is more plentiful.

Note:
It's important to understand that D-glucose is a naturally occurring sugar, whereas L-glucose is not but may be synthesised in the lab. You should also keep in mind that L-glucose cannot be phosphorylated by hexokinase, hence it cannot be utilised by living organisms.
The atoms in D-glucose and L-glucose are the same. Fischer projection reveals the only difference between the two structures. In Fischer projection, the oxygen and hydrogen group of atoms in L-glucose point to the left, unlike D-glucose. If these two molecules were to face each other, they would appear to be a mirror image of each other.