How many significant digits are 6.3590x10 7 mm

If you go by the decimal there should be 5 significant digits because 0 is a trailing zero and matters since it comes after a decimal. however if you do 

6.3590 x 10 ^7 = 63590000 then you would only have 4 significant digits because there is no longer a decimal to make the zero after the 9, significant. 

Hope this helps!

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na