Puzzle 2

123456
Across
  1. 4. What type of cloud has a flat top and is associated with severe weather?
  2. 6. What is the fourth step in the scientific method?
Down
  1. 1. What is the 5th planet in our solar system?
  2. 2. What is the center of an atom?
  3. 3. What type of matter does water change to when boiled?
  4. 5. What is the powerhouse of a cell?