400 multiplied by 10 is 4,000.
The equation needed is: V=fl Where V is the speed, f is the frequency and l is the wavelength. (the poxy thing won't let me enter a lamba sign) The key bit of information is "in a vacuum"; all waves in a vacuum travel at the same speed, 3x108ms-1. This is more commenly refered to as the speed of light, C. Therefore, f = V / l= C / l = 3x108 / 400x10-9 = 7.5x1014 Hz (Not in standard form that's: 750,000,000,000,000 Hz) (The '/' means divided by)
To find the number of moles in 80.00g of NaOH, you need to divide the mass in grams by the molar mass of NaOH. The molar mass of NaOH is 40 g/mol (sodium: 23g/mol, oxygen: 16g/mol, hydrogen: 1g/mol). Therefore, 80.00g / 40 g/mol = 2 moles of NaOH.