Explanation:
(a)
The relation between frequency and wavelength is shown below as:
c is the speed of light having value 
Given, Wavelength = 505 nm
Also, 1 m = 
nm
So,
Wavelength = 
m
Thus, Frequency is:
(b)
Also, 
Where,
h is Plank's constant having value 
c is the speed of light having value
So,
(c)
Electromagnetic spectrum is range of the frequencies and their respective wavelengths of the various type of the electromagnetic radiation.
In order of the increasing frequency and the photon energy and the decreasing wavelength the spectrum are:
Red , Orange, Yellow, Green, Blue, Indigo, Violet
Increasing wavelength is the opposite trend. Thus, The longest visible wavelength is red and the shortest is violet.
0.761 mol of 
would you have if you have 76.36 grams.
<h3>What is a mole?</h3>
A mole is defined as 6.02214076 × 
of some chemical unit, be it atoms, molecules, ions, or others. The mole is a convenient unit to use because of the great number of atoms, molecules, or others in any substance.
Given data:
Mass=76.36 grams
Moles = 0.761
Hence, 0.761 mol of would you have if you have 76.36 grams.
Learn more about moles here:
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Formaldehyde is an organic compound.
1. 100.67
2. 168.55
3. 2.747
So I’m not sure if 2 or 3 are right sorry
Answer: Option (b) is the correct answer.
Explanation:
It is known that metals are the species which readily lose an electron and tend to attain a positive charge.
For example, atomic number of sodium is 11 and its is an alkali metal. It electronic distribution is 2, 8, 1.
And, in order to attain stability it readily loses an electron and thus it become 
ion.
Also, it is known that species which tend to transfer or donate their valence electrons to other atoms tend to form ionic bond and the compound formed is known as ionic compound.
Therefore, we can conclude that the statement metal atoms held together by ionic bonds best describes a metal solid.
