The formula of kernite or razorite is

Options

A. `Na_2 B_4 O _7 . 4H_2 O `
B. `Na_3 BO_3 . 4H_2 O `
C. `Na_2 B_4 O_7. 10 H_2 O `
D. `Na_3 BO_3 . 10 H_2 O `

Answer

To determine the formula of kernite (also known as razorite), we can follow these steps:

### Step 1: Identify the mineral type
Kernite is a mineral that belongs to the boron family. It is important to recognize that it is a boron compound.

**Hint:** Look for minerals that are associated with boron to narrow down your options.

### Step 2: Research the chemical composition
Kernite is known to have a specific chemical formula. The formula for kernite is based on its constituent elements, which include sodium (Na), boron (B), and oxygen (O).

**Hint:** Consider the common oxidation states of the elements involved when determining the formula.

### Step 3: Write the formula
The correct formula for kernite is Na2B4O7·4H2O. This indicates that kernite contains two sodium atoms, four boron atoms, and seven oxygen atoms, along with four water molecules (indicating it is a hydrate).

**Hint:** Hydrates are often indicated by a dot followed by the number of water molecules.

### Step 4: Verify the options
Given the options provided in the question, we can confirm that Na2B4O7·4H2O is indeed the correct formula for kernite. Other options such as Na3B4O3·4H2O and Na2B4O7·10H2O are not correct.

**Hint:** Cross-check each option against known chemical formulas of boron minerals.

### Final Answer
The formula of kernite (or razorite) is Na2B4O7·4H2O.

---