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].
How many kilograms are in a metric ton? To differentiate between the different tons, the system has come up with the long ton, tonne and short ton. The long ton weighs 2,240 pounds, the tonne weighs 1,000 kilograms (2,204.6 pounds) and the short ton weighs 2,000 pounds (907.2 kilograms). The long ton and the tonne are commonly used in the United Kingdom for trade. The short ton is used in the United States.