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a. 3.8 x 10¹⁴ s⁻¹

Explanation:

For the first line,

we have wavelength = λ = 7.9 x 10⁻⁷ m

We know that , speed of light , c is given by:

                    c = λ x ν

             Where  λ is wavelength of the line and  ν is the frequency

So , the frequency , ν = c / λ = 3 x 10⁸ / 7.9 x 10⁻⁷ = 3.79 x 10¹⁴ s⁻¹

                                                                                 ≈  3.8 x 10¹⁴ s⁻¹

Therefore the frequency is 3.8 x 10¹⁴ s⁻¹ .

answer: -

reaction:

na + cl ⇌ nacl

balanced chemical equation:

na + 2cl ⇌ nacl2

sodium + clorine goes to form sodium chloride (table salt).

the product is nacl2.

and the reactants are na and cl.

(note: if you don’t know what ⇌ means, read below: -

⇌(double head arrow) means reversible reaction).