Answer: Option C
When two trains are moving in opposite directions, the speed of the relative motion of the two trains is equal to the sum of their speeds. The time taken by the two trains to cross each other completely is given by the formula:
Time = (sum of lengths of the trains) / (sum of their speeds)
In this case, the lengths of the two trains are given as 250 meters each, and their speeds are given as 80 kmph and 70 kmph respectively. To use the formula, we need to convert the speeds to meters per second, and also convert the units of the lengths to meters:

• Speed of first train = 80 kmph = (80 x 1000) / 3600 m/s = 22.22 m/s
• Speed of second train = 70 kmph = (70 x 1000) / 3600 m/s = 19.44 m/s
• Length of each train = 250 meters

Now we can substitute these values into the formula:
Time = (sum of lengths of the trains) / (sum of their speeds)= (250 + 250) / (22.22 + 19.44) seconds= 500 / 41.66 seconds= 11.999 seconds (approx.)
Rounding off to the nearest whole number, we get the answer as option C, 12 seconds.
Hence, the correct answer to the given question is option C, 12 seconds.