No, that's not true. All planets, moons, and stars have gravity. Actually all objects have gravity, it's just not very strong for small objects.
I'm not sure if it's half or not, probably less, but the only possibility would be Mercury. True. Mercury is the only one. Gravity on Mercury's surface is 37% of what it is on Earth. Except for Mars, where it's 38% of its value on Earth. Mercury and Mars are the only ones. Except for Pluto, where it's 4% of its value on Earth.
Well sometimes it is and sometimes it isn't. That old saying is not nessary true. Because there are plenty of planets in the universe that are the same size as earth but have less gravity than earth.
True. Gravity on the moon is about one-sixth that of Earth's gravity.
No. The gravity on Venus is only slightly less than it is on Earth. Venus has an atmosphere about 90 times denser than Earth's.
earth rotation on its axis causes gravity to occur on earth
No, gravity doesn't cause the Earth's rotation.
Earth pulls on the object, and the object pulls on Earth
NO!
true
For the most part, yes. But the actual determining factor for how much gravity a planet has is based on its mass, and since size and mass are often related it is somewhat accurate to say that the bigger the planet is, the more gravity it will have.
A planet must be large enough for its gravity to pull it into a nearly round shape. In our solar system, a planet needs to have cleared its orbit of other debris to be considered a true planet.
True. Air particles are pulled towards Earth's surface by the force of gravity, which creates atmospheric pressure.