molar mass of methane CH4
= C + 4 H
= 12.0 + 4 x 1.008
= 12.0 + 4.032
= 16.042g/mol
7.31 x 10^25 molecules x <u> 1 mole CH4 </u> = 121.43 moles
6.02 x 10^23 CH4 molecules
121.43 moles CH4 are present.
Answer:

Explanation:
The relation between frequency and wavelength is shown below as:

c is the speed of light having value 
Given, Frequency = 1290 kHz =
(As 1 kHz = 1000 Hz )
Thus, Wavelength is:



It is physical change because ? has changed alone not with chemicals