Which phylum is the largest phylum of the animal kingdom?

Which of the following sets of organisms is correctly classified?

$S$ - Statement: Malpighian tubules are the excretory organs in $Arthropoda$.
$R$ - Reason: $Arthropoda$ belongs to the phylum $Mollusca$.

Which of the following is true for sandfly,scorpion,cockroach,and silverfish?

In which animals is an open circulatory system seen?

Crayfish is a