@AlanTal saidAnswer to both questions: Mercury, on average.
S M V E M J S U N
Above is a crib for our solar system, in the order away from the sun, namely:
Sun, Mercury, Venus etc.
Question 1:
Which planet is closest, on average*, to Earth?
*over a full Earth year.
Question 2:
As above, but this time closest to Neptune, over a full Neptune year.
All other planets spend far more time much further from the other planets.