Question

Condition for the line ax+by+c=0 be parallel to y axis

Answer 1

Condition for the line to be parallel to y axis would be:
b = 0.

Answer 2

Since the line is parallel to Y-axis therefore the slope would not be defined( as it intersects X-axis at an angle of 90°).

The x co-ordinate would always be constant.

Therefore the equation of the line would be

ax+c=0