Assertion (A): People who have been caught in a natural disaster (such as tsunami) or have been victims of bomb blasts by terrorists, or been in a serious accident or in a war-related situation, experience post-traumatic stress disorder (PTSD).
Reason (R) : PTSD symptoms may include recurrent dreams, flashbacks, impaired concentration, and emotional numbing.

Both A and R are true, but R is not the correct explanation of A

The correct answer is Option:

Assertion (A): People who have been caught in a natural disaster (such as tsunami) or have been victims of bomb blasts by terrorists, or been in a serious accident or in a war-related situation, experience post-traumatic stress disorder (PTSD). This is correct.
Reason (R) : PTSD symptoms may include recurrent dreams, flashbacks, impaired concentration, and emotional numbing. This is also correct.

While both the assertion and the reason are true statements, the reason (R) does not directly explain why people who have experienced traumatic events may develop post-traumatic stress disorder (PTSD). The reason simply provides additional information about the symptoms of PTSD, rather than explaining why certain events lead to the development of PTSD.