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].
1 ton (t) is equal to 2204.62262185 pounds (lbs). 1 t = 2204.62262185 lb. The mass m in pounds (lb) is equal to the mass m in tons (t) divided by 0.00045359237: m(lb) = m(t) / 0.00045359237. Convert 5t to pounds: m(lb) = 5 t / 0.00045359237 = 11023 lb.