They both have the same mass.
A kilogram is a kilogram, no matter what.
It's the same weight
A kilogram of sand takes up much less space than a kilogram of feathers because sand is denser than feathers. Density refers to how much mass is contained in a given volume. Since sand particles are heavier and more compact than feathers, they occupy less space for the same mass.
A kilogram
A kilogram is heavier.
A kilogram is a kilogram, no matter what.
It's the same weight
Neither of the above BOTH ARE EQUAL
No. A kilogram is a kilogram is a kilogram. On the other hand, a kilogram of sand will most likely be a different size than a kilogram of gravel. We are told by the question though that they both weigh one kilogram, so they are the same weight.
Due to atmospheric pressure the weight of 10 kg of cotton is grater than 10 kg of iron.
I don't know what "appears heavier" means. A kilogram of mass is a kilogram of mass. Appearance has nothing to do with it. The cotton is (probably) less dense than the iron and will occupy a larger volume, but that doesn't have anything to do with the vacuum part.
A kilogram of sand takes up much less space than a kilogram of feathers because sand is denser than feathers. Density refers to how much mass is contained in a given volume. Since sand particles are heavier and more compact than feathers, they occupy less space for the same mass.
A kilogram
A kilogram is heavier.
A kilogram is about 2.2 times heavier than a pound.
Cotton is a very lightweight plant, and fabric. Metal is much heavier than cotton.
Both the same 10kg is 10kg no matter what it is made of bricks or cotton wool or wood or sand, and so on ...