When to make up missed prayers

[He] was ill and they did surgery on him; [as a result] he missed a number of obligatory prayers, so is he required to pray them all together once he has recovered, or should he pray all these obligatory prayers at their appointed times, such as [making-up] the [missed] ‘asr [prayer] at the time of the ‘asr prayer, and the [missed] zhuhr [prayer] at the time of the zhuhr prayer, and the [missed] maghrib [prayer] at the time of the maghrib prayer, and so on?

Missed the prayer for rain

With regard to the prayer for rain, if a group [of people] enter [the masjid] and [find] the imaam is giving the sermon, after already having just completed the two rak’ah prayer [for rain in congregation], should they [now] offer the prayer [for rain themselves] or should they sit down [with the rest of the congregation] for the sermon? Also, is [the rain prayer] to be made up [if missed]? And [if it is], should they offer the prayer in congregation?