The v - x equation from the given graph can be written as

$v=(-\genfrac{}{}{0.1ex}{}{v_0}{x_0})x+v_0$... (i)
 
$a=\genfrac{}{}{0.1ex}{}{dv}{dt}=(-\genfrac{}{}{0.1ex}{}{v_0}{x_0})\genfrac{}{}{0.1ex}{}{dx}{dt}$
 
$=(-\genfrac{}{}{0.1ex}{}{v_0}{x_0})v$
 
Substituting v from Eq. (i) we get,

$a=(-\genfrac{}{}{0.1ex}{}{v_0}{x_0})[(-\genfrac{}{}{0.1ex}{}{v_0}{x_0})x+v_0]$
 
$a={\left(\genfrac{}{}{0.1ex}{}{v_0}{x_0}\right)}^{2}x-\genfrac{}{}{0.1ex}{}{v_0^2}{x_0}$
 
Thus, a-x graph is a straight line with positive slope and negative intercept.
Correct answer is