When heated an iron bar expands by 0.2 %.if the increase in length 1 cm, what is the original length of the bar?

0.2% = 2/100

increase amount over the whole amount

If the increase length is 1cm and you are looking for the whole amount

2/100 = 1/x

Cross multiply
2x = 100
x = 50 cm is the original length of the bar

Checking you answer,
0.2% of 50 is 0.02 × 50 which is 1 so the answer is correct.

The original length of the bar is 50 cm.

What's the denominator

I'm sure the answer is a