Answer:
Line segment PP'is parallel to the y-axis.
Line segment PP'is perpendicular to the x-axis.
The distance from P to the x-axis is equal to the distance from P'to the x-axis.
Step-by-step explanation:
Given:
Point P is in 1st quadrant and P' is its reflection across x axis.
The figure for the given scenario is given below.
From the figure, following points are clear:
1. Line segment PP' is parallel to y axis (Vertical axis).
2. Line segment PP' is perpendicular to x axis (Horizontal axis).
Now, when we reflect a point across the x axis, the co-ordinate rule states that: 
So, the value of y changes sign. So, vertical distance of the original point is same as that of the reflected point. The only difference is one is above x axis and the other below x axis.
Therefore, the distance from P to the x-axis is equal to the distance from P'to the x-axis.
So, the statements that are true are as follows:
Line segment PP'is parallel to the y-axis.
Line segment PP'is perpendicular to the x-axis.
The distance from P to the x-axis is equal to the distance from P' to the x-axis.