Answer:- Frequency is 
.
Solution:- The wavelength of electromagnetic radiation is given as 625 nm and we are asked to calculate the frequency. Frequency is inversely proportional to the wavelength and the formula used to calculate frequency when wavelength is given is:
where, 
is frequency, c is speed of light and 
is the wavelength.
Value of speed of light is 
. We need to convert the given wavelength from nm to m.
So, 
= 
Let's plug in the values in the formula and calculate the frequency:
= 
or Hz.
So, the frequency of the electromagnetic wave is .
i will ans the 2nd part first:
heat sources 4 homes: those wuld be renewable resources that generate heat. They include geothermal, solar water-heating and bio-mass.
primarily produce electricity: those wuld be something that is big like a dam for hydroelectric, wind turbine for electric generation, and solar farm for electricity.
