Answer : The correct option is, 0.21 moles
Solution : Given,
Molarity of the solution = 0.85 M = 0.85 mole/L
Volume of solution = 250 ml = 0.25 L 
Molarity : It is defined as the number of moles of solute present in one liter of the solution.
Formula used :

Now put all the given values in this formula, we get the moles of solute of the solution.


Therefore, the moles of solute is, 0.21 moles
A chemical change is a change that results in new chemicals (the reactants underwent a chemical change which resulted in new products).
an example of a chemical change is the burning of paper. An example of something that is not a chemical change is the melting of ice.
Keep in mind that atomic number is the number of protons in the atom of the element. Therefore, in the case where there are 78 protons, we can conclude that the atomic number of this element is ALSO 78.
Let me know if you need anything else.
- Dotz
Prediction, control and experiment
Answer:
The answer is

Explanation:
The frequency of the photon can be found by using the formula

where
E is the energy
f is the frequency
h is the Planck's constant which is
6.626 × 10-³⁴ Js
From the question
E = 2.50 × 10^-18 J
So we have

We have the final answer as

Hope this helps you