Here's how to calculate the number of moles in 0.025 g of ammonium dichromate (NH₄₂Cr₂O₇):

1. Calculate the molar mass of NH₄₂Cr₂O₇

* Molar mass of N = 14.01 g/mol

* Molar mass of H = 1.01 g/mol

* Molar mass of Cr = 52.00 g/mol

* Molar mass of O = 16.00 g/mol

Molar mass of NH₄₂Cr₂O₇ = (2 * 14.01) + (8 * 1.01) + (2 * 52.00) + (7 * 16.00) = 252.08 g/mol

2. Use the formula: moles = mass / molar mass

* moles = 0.025 g / 252.08 g/mol

* moles ≈ 0.0001 mol

Therefore, there are approximately 0.0001 moles in 0.025 g of ammonium dichromate.