Mole Fraction Calculations in Solutions

Which of the following best defines the mole fraction ($X$) of a component in a solution?

Given 25.0 g of dichloromethane ($\mathrm{CH_2Cl_2}$) dissolved in 125 g of water, what is the mole fraction of dichloromethane? (Molar masses: $\mathrm{CH_2Cl_2} = 84.93\ \mathrm{g/mol}$, $\mathrm{H_2O} = 18.02\ \mathrm{g/mol}$)

A reaction vessel contains 20.3 g $\mathrm{Cl_2}$, 4.27 g $\mathrm{Ne}$, and 10.8 g $\mathrm{O_2}$. What is the mole fraction of nitrogen if 5.00 g $\mathrm{N_2}$ is also present? (Molar masses: $\mathrm{Cl_2} = 70.90\ \mathrm{g/mol}$, $\mathrm{Ne} = 20.18\ \mathrm{g/mol}$, $\mathrm{O_2} = 32.00\ \mathrm{g/mol}$, $\mathrm{N_2} = 28.02\ \mathrm{g/mol}$)