What are $P$ and $Q$ in the given structure?

Which of the following immunoglobulins constitutes the largest percentage in human milk?

The antibodies are:

Transfer of antibodies from mother to infant through colostrum after birth provides . . . . . . to the baby.

Which of the following represents the property of immunoglobulins?

Person '$A$' cannot step out of his house. He has to spend his entire life in sterile isolation; otherwise, he would quickly contract a fatal infection. This person has almost no effective immune system. This disease is also called '$baby$ $in$ $a$ $bubble$ $syndrome$'. Identify the disease this person '$A$' is suffering from.