Is a straight angle also an obtuse angle ?? 

No, a straight angle can not be an obtuse angle because the measure of obtuse angle is between 90? to 180? not less than 91? and not more than 179?and the measure of straight angle is only 180? and not less than 180? and not more than 180?.

Obtuse angle=91?,92?,178?,179? etc.
Right angle=90?
Straight angle=180?

No a straight angle cannot be obtuse is angle because obtuse angles are more than 90 but less than 180 degree.
For example, consider 90.1- it is the smallest obtuse angle.
And considered 179.9 it is the largest obtuse angle.

So no a straight angle cannot be a objective is angle.

Acute angle- more than zero less than 90 degree.
Obtuse angle- more than 90 degree less than 180 degree.
Reflex angle- more than 180 less than 360 degree.
Right angle- exactly 90 degree
Straight angle- exactly 180 degree.
Complete angle- exactly 360 degree.