The threshold photoelectric effects in tungsten is produced by light of a wavelength 260 nm give the energy of a photon of this light in joules.

Energy of light is

Explanation:

Given:

Wavelength

Also we know the speed of light

To calculate frequency of light , divide speed of light by Wavelength

Hence frequency is

Now, To calculate energy (E), we need to multiply planks's constant with the frequency of light  .

Also Plank's Constant =

Hence Energy of light is

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

it's c. elements are placed in rows based on how may valencies electrons have.