The value of n in the molecular formula BenAl2Si6O18 is

The correct option is 3.

To find the value of n in the molecular formula of the mineral beryl, Be_nAl₂Si₆O₁₈, we can use the concept of chemical charge neutrality. A stable, neutral compound has a total net charge of zero. By summing the charges of all individual ions in the formula according to their common oxidation states, we can solve for n.

Let's identify the standard oxidation states for each element present in the compound:
• Beryllium (Be) belongs to Group 2 (alkaline earth metals) and has an oxidation state of +2.
• Aluminum (Al) is a Group 13 metal and has an oxidation state of +3.
• Silicon (Si) has an oxidation state of +4 in silicate minerals.
• Oxygen (O) has a standard oxidation state of -2.

Using these values, we set up the equation for the total charge of the molecule, which must equal zero:

$$n\times (+2)+2\times (+3)+6\times (+4)+18\times (-2)=0$$

Now, simplify the terms inside the equation step-by-step:

$$2n+6+24-36=0$$

Combine the constant values:

$$2n-6=0$$

Solve for n:

$$2n=6$$

$$n=3$$

Thus, the value of n is 3, corresponding to the chemical formula of beryl: Be₃Al₂Si₆O₁₈.