What are the first cells to arrive at a bacterial infection

Neutrophils

Explanation:

High neutrophils in the blood count can be a sign of bacterial or fungal infection. That's because neutrophils are the first cells to reach a bacterial infection. Neutrophils are a type of white blood cell, blood defense cells that participate in fighting infections caused by fungi and bacteria.

However, the number of neutrophils can also be high in cases of inflammation, tumor, bleeding, use of certain medications, among others.

Neutrophil levels may also be elevated in some temporary situations, such as infarction, after intense physical exercise, postoperatively, medication use (lithium, corticosteroids, epinephrine), smoking, pregnancy and newborns in the first days after delivery.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds