Choices 'a', 'c', and 'd' are true.
In choice 'b', I'm not sure what it means when it says that masses
are 'balanced'. To me, masses are only balanced when they're on
a see-saw, or on opposite ends of a rope that goes over a pulley.
Maybe the statement means that the mass of the nucleus and the
mass of the electron cloud are equal. This is way false. It takes
more than 1,800 electrons to make the mass of ONE proton or
neutron, and the most complex atom in nature only has 92 electrons
in it. So there's no way that the masses of the nucleus and the electrons
in one atom could ever be anywhere near equal.
Answer:

Explanation:
From the question we are told that
The electric filed is
Generally according to Gauss law
=> 
Given that the electric field is pointing downward , the equation become

Here
is the excess charge on the surface of the earth
is the surface area of the of the earth which is mathematically represented as

Where r is the radius of the earth which has a value 
substituting values


So

Here
s the permitivity of free space with value

substituting values


Answer:
A because it was rejected as it cannot become a law it was totally wrong as compared to today's information about out universe that how big bang theory was there.... So it is right the option A
Answer:
W = 735.75[J]
Explanation:
Work is defined as the product of force by distance. Therefore we can use the following equation.

where:
W = work [J] (units of Joules)
F = force [N] (units of Newtons)
d = distance = 3 [m]
But first, we must determine the force that is equal to the product of mass by gravity (weight of the body).
![F=m*g\\F=25*9.81\\F=245.25[N]](https://tex.z-dn.net/?f=F%3Dm%2Ag%5C%5CF%3D25%2A9.81%5C%5CF%3D245.25%5BN%5D)
![W=F*d\\W=245.25*3\\W=735.75[J]](https://tex.z-dn.net/?f=W%3DF%2Ad%5C%5CW%3D245.25%2A3%5C%5CW%3D735.75%5BJ%5D)
So, option 3 or the ambulance sound waves have more waves and shorter wavelength is the correct reason for ambulance siren having higher pitch compared to fire truck siren
Explanation:
Pitch of any sound wave is determined as the clarity in frequency of notes or the number of times a cycle is repeated for a single second. So pitch is similar to frequency. And frequency is the measure of number of complete cycles in a second. So if the ambulance siren has higher pitch compared to siren of fire truck. Then this means the frequency of ambulance siren is greater than the fire truck siren. As the frequency is more, then from the given options, choice 3 is correct. The ambulance siren have more waves and shorter wavelength. As more the frequency or number of waves, lesser or shorter is the wavelength of sound wave from ambulance.