SMO 2011 Junior Round 1 Question 4

Question 4

Let $$x=1\underbrace{00\cdots0}_{2011}\,1\underbrace{00\cdots0}_{2012}\,50.$$
The two indicated blocks contain $2011$ and $2012$ zeros, respectively. Which of the following is a perfect square?

$x-75$
$x-25$
$x$
$x+25$
$x+75$