Explain why newton’s first law of motion can be difficult to observe in moving objects?

That's because in our daily life in the real world, nobody has EVER seen an object that's in constant uniform motion without any net force acting on it.

EVERY object we've ever seen has gravity acting on it, buoyancy due to the air surrounding it, plus friction and air resistance if it's moving.

To all of our senses and observations, the First Law of Motion should be:

"An object in motion, with no force applied to keep it going, stops."

Except that's wrong.

  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

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it