Answer: Immunity

Answer: A prickle

Answer: Hydrogen

Answer: False

Answer: 99%

Answer: The black widow

Answer: A perfect number.
You might also think of a perfect number as a number that is half the sum of all of its positive divisors, including itself! This definition is at least 2300 years old as it appears in Euclid's "Elements".

Answer: Neptune

Answer: 9,000

Answer: Sir Isaac Newton