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1.Atomic Number (Z) = Mass Number (A) - Number of Neutrons

neutrons = mass number-atomic number

Atomic mass Cl-37= 17

Mass number Cl-37=37

Neutrons = 37-17=20

2. Mass atom X = mass isotope 1 . % + mass isotope 2.%...

3. The energy in one photon can be formulated as

f = c / λ, so :

Energy is directly proportional to frequency and inversely proportional to the wavelength

So, as the frequency of photon increases, the energy of photon increases

4. Based on answer number 3 :

A. The wavelength becomes longer, and the energy decreases

the molecules move in straight line until they collide with each other or with the walls of the container. collisions are perfectly elastic; when two molecules collide, they change their directions and kinetic energies, but the total kinetic energy is conserved.

explanation:

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.