Answer:1). Distance of far point x=0.9m
Therefore, since the image is virtual
-f=-x = -0.9m
Power of the concave lenses = 1/f = 1/-0.9
= -1.11D
2 ) near point is 21cm = 0.21m
Power = 4-1/near point
= 4/0.21
= 14.2D.
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50N is your force and the acceleration is -9.8m/s^2 due to gravity.
So, you just plug that in.

BUT you know that mass cannot be negative, so you just disregard the negative sign and the mass of the rock is 5.102 grams.
Similarities:
The halogens like noble gases are gaseous im nature. Example,
Chlorine, bromine are halogens and argon , xenon are noble gases.
Both are non-metals.
Differences: Halogens are very reactive because their octet needs only one electron tk complete. But, the nobles gases are quite stable and unreactive because the have complete octets.
We are given
E = <span>2.64 × 10-21 J
h = </span><span>6.6 × 10-34 J s
The options given below are frequencies, therefore, the question must be asking about the frequency fo the given wave
The equation is
E = h f
Simply substitute and solve for f which is the frequency
f = </span>2.64 × 10-21 J / 6.6 × 10-34 J s
f = <span>4.00 × 1012<span> hertz</span></span>