In a controlled experiment why is it important to change just one variable parameter at a time

These models show the electron structures of two different nonmetal elements. which element is likely more reactive, and why? element 1 is more reactive because it has fewer electron shells and is toward the top of its group on the periodic table. element 1 is more reactive because it has more electrons in its valence shell and is farther to the right on the periodic table. element 2 is more reactive because it does not have a valence shell close to the nucleus, so it will attract electrons. element 2 is more reactive because it does not have a full valence shell, so it will attract electrons.

** urgent** the voltage across the primary winding is 350,000 v, and the voltage across the secondary winding is 17,500 v. if the secondary winding has 600 coils, how many coils are in the primary winding? a- 30 coilsb- 583 coilsc- 12,000 coilsd- 332,500 coils

If the spring constant k of a pogo stick is 3500 n m and the weight of the person on the pogo stick is 700 n, how much is the spring in the botom of the pogo stick compressed?