Hey,

The answer is No. IGNOU has only one exam annually. There is no semester system. The exams are conducted twice a year July and December. You have to appear for any one of them.

Now about your second question. Since you have failed to attempt July examination, you can appear in December examination. Any student who fails in exam or couldn't attempt the exam 1 is eligible to appear for exam 2 (December).

Hope this helps!