Which of these changes is a chemical change? A. A block of ice forms liquid water when salt is sprinkled on it.
B. A block of ice is crushed into small pieces.
C. A block of ice melts when heated.
D. A block of ice fizzes and forms a gas when sodium is sprinkled on
it.
please help :)

weight of any object is given by

w = m*g

where m is mass of the object and g is the acceleration due to gravity.

for earth the value of g is 9.8 m/s^2 so

w=117.6 n m=12 g=?

117.6=12g => g=9.8 m/s^2

which is the force of gravity on earth.

alchemy hadn't scientific methods of study, appeal to mysticism and fantasy, the knowledge of chemistry and physics were modest at that time.

alchemy was - but as new rules were discovered it either changed into chemistry or it became "unscientific".