Depends on where the object is. On earth, moon , or somewhere without any other mass (theoretically). I think you mean how much does weigh on earth. So, the average gravitational acceleration on earth is : 9.83 m/s^2 To find out how much an object weighs, this is the formula : G=m.g where m is mass of the object g is the gravitational acceleration and G is weight. So, G = 10.9,83 = 98,3 N is the answer.
The statement that the friend made is not true. most of the mass of the plant is from carbon. the carbon comes from carbon dioxide which is used during photosynthesis. the left over carbon from photosynthesis is used to to help the plant gain mass. there is a process for this which is called cellular respiration
Which property of gas affects the gas by change in that property ?