Non-contact forces differ from contact forces in the way they act between objects. Here is a breakdown of the statements you provided:
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Non-contact forces are always present: This can be somewhat misleading. Non-contact forces (like gravitational, electromagnetic, and nuclear forces) do exist without direct contact between objects, but they are not always "active" or "noticeable." They can influence objects depending on their proximity and the nature of the interaction.
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Contact forces behave differently in space: This statement touches on the fact that contact forces (like friction or tension) require physical contact between objects and do not operate in a vacuum like non-contact forces. In space, without contact, only non-contact forces can have an effect.
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Contact forces can be exerted through objects: This is primarily a misunderstanding. Contact forces generally require direct contact; however, they can be transmitted through materials (like tension in a rope), but without that contact at some point, they cannot exert force.
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Non-contact forces can only be attractive: This statement is not accurate. While many non-contact forces (like gravity) are indeed attractive, there are also non-contact forces that can be repulsive, such as electromagnetic forces (like the force between like charges).
In summary, the key difference is that contact forces require objects to be physically touching to exert force, while non-contact forces can act over a distance without direct contact.