Is the iddah (waiting period) obligatory for a wife who has had her marriage contract solemnized but has not been consummated, given that there was a complete khalwa (private seclusion) between them, and is it permissible for the husband to take her back after divorcing her?

Proper seclusion is equivalent to consummation, thereby obligating the full Mahr. It also necessitates the waiting period (iddah) if a divorce occurs. Divorce after proper seclusion is considered revocable (raji) according to the Hanbalis, and this is the relied-upon opinion. Therefore, the wife can be taken back as long as she is within her waiting period.