Which two samples of gas at stp contain the same total number of molecules?
(1) 1 l of co(g) and 0.5 l of n2(g)
(2) 2 l of co(g) and 0.5 l of nh3(g)
(3) 1 l of h2(g) and 2 l of cl2(g)
(4) 2 l of h2(g) and 2 l of cl2(g)

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.