If for a reaction in which A(g) converts to B(g) the reaction carried out at const. 

V & T results into the following graph. 

 

 

 

then the reaction must be $\mathrm{A}\left(\mathrm{g}\right)\to 3\mathrm{B}\left(\mathrm{g}\right)$ and is a zero-order reactoin. 

then the reaction must be $\mathrm{A}\left(\mathrm{g}\right)\to 3\mathrm{B}\left(\mathrm{g}\right)$ and is a first-order reaction. 

then the reaction must be $\mathrm{A}\left(\mathrm{g}\right)\to 3\mathrm{B}\left(\mathrm{g}\right)$ and is a first-order reaction.

then the reaction must be $\mathrm{A}\left(\mathrm{g}\right)\to 3\mathrm{B}\left(\mathrm{g}\right)$ and is a second-order reactoin.