volume of Ni = 25 nL = 25 x 10⁻⁹ L
mol Ni = 25 x 10⁻⁹ L x 1.25 mol/L = 3.125 x 10⁻⁸
mass = mol x Ar Ni
mass = 3.125 x 10⁻⁸ x 59 g/mol
mass = 1.84 x 10⁻⁶ g = 1.84 μg
We will assume helium to behave as an ideal gas and apply the ideal gas law:
PV = nRT
For pressure measured in atmospheres and volume measured in liters, the value of the molar gas constant is 0.082. Therefore:
T = PV / nR
T = (2.57 x 15.5) / (1.2 x 0.082)
T = 404.8 Kelvin