Which of the following is the function of $T-$cells?

Select the lymphoid organs from the given choices:
$I$. Lymph node $II$. Thymus gland
$III$. Red bone marrow $IV$. Liver
$V$. Spleen $VI$. Osteocytes
$VII$. Peyer's patches
The correct option is:

An antigen is

Transplantation of tissues/organs often fails due to non-acceptance by the patient's body. Which type of immune response is responsible for such rejections?

Which of the following is $NOT$ an immunoglobulin found in serum?

Identify the correct statements from the following:
$(i)$ The skin is the main physical barrier.
$(ii)$ Mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts is a physiological barrier.
$(iii)$ $IgA, IgM, IgE, IgG$ are types of $T$-cells.
$(iv)$ The primary immune response is very intense.