Which of the following is used to obtain `alpha`-form of glucose?

Options

A. It is obtained by the crystallisation from concentrated solution of glucose at 317 K
B. It is obtained by the crystallisation from concentrated solution of glucose at 303 K
C. It is obtained by the crystallisation from hot saturated aqueous solution at 303 K
D. It is obtained by the crystallisation from hot and saturated aqueous solution at 371 K

Explanation

To determine which method is used to obtain the alpha-form of glucose, we need to understand the crystallization process and the specific conditions required for this transformation. Here’s a step-by-step solution:

### Step 1: Understanding the Forms of Glucose
Glucose exists in two anomeric forms: alpha (α) and beta (β). The distinction between these forms lies in the position of the hydroxyl group (-OH) on the anomeric carbon (C1). In the alpha form, the -OH group is positioned below the plane of the ring, while in the beta form, it is above the plane.

**Hint for Step 1:** Remember the structural difference between alpha and beta forms of glucose, focusing on the anomeric carbon.

### Step 2: Identifying the Crystallization Conditions
The crystallization of glucose is temperature-dependent. The question specifies that we need to find the conditions under which the alpha form of glucose is obtained. According to standard references, the crystallization of glucose to obtain the alpha form occurs at a specific temperature.

**Hint for Step 2:** Look for temperature-specific conditions in the literature or textbooks that mention the crystallization of glucose.

### Step 3: Analyzing the Options
We are provided with several options regarding the conditions for crystallization. The key detail is that the crystallization must occur at 303 Kelvin, which is known to yield the alpha-D-glucose.

**Hint for Step 3:** Pay attention to the temperature mentioned in each option, as it is crucial for determining the correct method.

### Step 4: Conclusion
After analyzing the options, we find that the correct method to obtain the alpha form of glucose is through the crystallization of a concentrated glucose solution at 303 Kelvin. This is supported by literature and is a well-documented reaction.

**Final Answer:** The correct option is **Option 2: Concentrated solution of glucose at 303 Kelvin**.