The electrostatic force between the two ions is 
Explanation:
The electrostatic force between two charged particle is given by Coulomb's law:

where
is the Coulomb's constant
are the two charges
r is the separation between the two charges
In this problem, the ion of sodium has a charge of

while the ion of chlorine has a charge of

And the distance between the two ions is

Substituting, we find the electrostatic force between the two ions:

where the negative sign simply means that the force is attractive, since the two ions have opposite charge.
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Answer:

Explanation:
The energy emitted by a single photon is given by:

where
h is the Planck constant
c is the speed of light
is the wavelength of the photon
For the photons emitted by the zinc atoms,

So the energy of a single photon emitted is

And since the number of atoms is

The total energy emitted will be

Answer:
False
Explanation:
Protons are positively charged, electrons are negatively charged, and neutrons have no charge.
Flammability because density is stating about magnesium something with melting point and magnetism but Flammability is stating how easily can it be changed into a new substance by using flame.
1) Focal length
We can find the focal length of the mirror by using the mirror equation:

(1)
where
f is the focal length

is the distance of the object from the mirror

is the distance of the image from the mirror
In this case,

, while

(the distance of the image should be taken as negative, because the image is to the right (behind) of the mirror, so it is virtual). If we use these data inside (1), we find the focal length of the mirror:

from which we find

2) The mirror is convex: in fact, for the sign convention, a concave mirror has positive focal length while a convex mirror has negative focal length. In this case, the focal length is negative, so the mirror is convex.
3) The image is virtual, because it is behind the mirror and in fact we have taken its distance from the mirror as negative.
4) The radius of curvature of a mirror is twice its focal length, so for the mirror in our problem the radius of curvature is: