Answer:
600K 
Step-by-step explanation:
The following were obtained from the question. 
Initial temperature (T1) = 300K 
Initial Volume (V1) = 0.1L
Final volume (V2) = 0.2L
Final temperature (T2) =? 
Step 2:
Determination of the final temperature.
Since the pressure is constant, the gas is simply obeying Charles' law.
Using the Charles' law equation, the final temperature can be obtained as follow:
V1/T1 = V2 /T2 
0.1/300 = 0.2/T2
Cross multiply to express in linear form 
0.1 x T2 = 300 x 0.2
Divide both side by 0.1
T2 = (300 x 0.2)/0.1
T2 = 600K