How many elements of actinoids including actinium are having no any electron in 5f subshell in their ground state?

The actinide series includes 15 elements from Actinium (Ac, atomic number 89) to Lawrencium (Lr, atomic number 103).

The electron configuration of Actinium (Ac) is [Rn] 6d1 7s2. This means that Actinium does not have any electron in the 5f subshell in its ground state.

The electron configuration of Thorium (Th, atomic number 90) is [Rn] 6d2 7s2. This means that Thorium also does not have any electron in the 5f subshell in its ground state.

The electron configuration of Protactinium (Pa, atomic number 91) is [Rn] 5f2 6d1 7s2. This means that Protactinium does have electrons in the 5f subshell in its ground state.

So, only Actinium and Thorium among the actinides do not have any electron in the 5f subshell in their ground state. Therefore, the answer is 2.