The Brainliest Answer!
I will list out the points for each:

g -
1. It is the acceleration due to gravity.
2. S.I. unit is m/s²
3. Its value varies from place to place.
4. Value of g on earth is 9.8m/s²

G -
1. It is the universal gravitational constant. (Numerically, it is defined as force of gravitation between two bodies of masses, each of 1kg kept 
at a distance of 1m from each other)
2. S.I. unit is Nm² or kg²
3. Its value is constant throughout the universe.
4. Value of G is 6.67 × 10^-11 Nm² or kg²

Hope I helped. Note: ^ refers to 'to the power of'
Please mark it as the best if its good.
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g is specific to a planet and it is acceleration.
G is a proportionality constant in the law of gravitation F = G m1 m2/d square
G=universal gravitational const                                                                                    2.its value=6.67 x10*-11NM2/Kg2                                                                                3.its value is const any where on the earth                                                                                                                                                                                                                             1.       g=accelelaration due to gravity                                                          2.g=9.8m/s2                                                                                                        3.its value varies from place to place ie maximum at poles and minimum at the equator                                                                                   
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please use the symbols like square or subscript or omega or theta etc. these are available in the buttons with labels in the answering window: Pi and omega