In the controlled experiment, a scientist is studying how long it takes parachutes of different sizes to fall to the ground. what are the manipulated/experimental variables?

The size of the parachutes.

Explanation: In this experiment we have two variables: The size of the parachute and the time that the parachute needs to cover a given distance (from a plane to the ground, for example)

The only thing that the scientist can modify, the independent variable, is the size of the parachute, and this will impact in the dependent variable, the time it needs to fall to the ground.

  the grams     of oxygen gas   that can be produced     is 20.6   grams of o₂

calculation

2liclo₃ →   2 licl + 3 o₂

step 1:   find the moles of liclo₃

moles = mass÷ molar mass

from periodic table the molar mass of liclo₃ =6.9 +35.5   +(16 x3) =90.4 g/mol

moles=38.7 g÷90.4 g/mol=0.4281   moles

step 2:   use the   mole ratio   to calculate the moles of o2

from equation above, liclo₃: o₂   is 2: 3  

therefore the moles of   o₂=0.4281 moles x3/2 =0.6422   moles

step 3: find mass   of o₂

mass= moles x molar mass

from periodic table the   molar mass of   o₂ = 16 x2= 32 g/mol

mass=0.6422   moles   x   32 g/mol = 20.6 grams of o₂