(a) the rms speed of the
molecules;

p
= 1/3 r<c^{2}>

1.0
× 10^{5 }Pa = 1/3 × 1.25 kg m-3 × <*c*^{2}>

<*c*^{2}>
= __3 × 1.0 × 10__^{5} Pa = 240 000 m^{2} s^{-2}

1.25 kg m^{-3}

Rms
speed = **490 m s**^{-1}

(b) the temperature at which
the molecules travel twice as fast.

Did
you forget to convert Celsius to Kelvin?