If you mean molecular oxygen, O2, then no, there is no more than trace amounts on Mars (compared to the Earth which has an atmosphere composed of over 20% O2). Our atmosphere is mostly nitrogen (N2) followed by oxygen (O2) with smaller amounts of argon and carbon dioxide.
A ton is 2000 pounds (907.19 kg), so does it follow that a half-ton truck weighs 1000 pounds (453.5 kg)? Actually, the name doesn't refer to the weight of the truck. In fact, half-ton pickups weigh much more than that. The weight of a truck without cargo or passengers is called the curb weight. For example, many 2007 half-ton pickups have curb weights between 9000 (4082.3 kg) and 11000 (4989.5 kg) pounds [source: Edmunds].
This could contain a volume between 175 and 213 imperial gallons (210 and 256 US gal), which could weigh around 2,000 pounds (910 kg) and occupy some 60 cubic feet (1.7 m3) of space. In the United Kingdom the ton is defined as 2,240 avoirdupois pounds (1,016 kg). From 1965 the UK embarked upon a programme of metrication and gradually introduced metric units, including the tonne (metric ton), defined as 1000 kg (2,204.6 lbs).