After a mosquito bites a human, it injects the malarial parasite (Plasmodium) into the bloodstream. From here, the parasite travels to the liver where it undergoes an initial phase of multiplication. This phase, known as the liver stage, takes place within the hepatocytes (liver cells) and lasts for several days. During this stage, the parasite reproduces asexually, resulting in the formation of several thousand daughter cells called merozoites.

After the liver stage, the merozoites are released into the bloodstream where they invade red blood cells. This marks the beginning of the blood stage of the infection. Inside the red blood cells, the merozoites multiply further, causing the cells to burst and release more parasites. This cycle of invasion, multiplication, and cell bursting leads to the characteristic symptoms of malaria, such as fever, chills, and anemia.

Based on this information, option 3 (liver) is the correct answer as it correctly identifies the location of the initial multiplication of the malarial parasites after entering the human body.