The electron configuration of Actinides are gives as

$(a)\;(4f)^{1-14}(5d)^{0-1} (6S)^2 \\(b)\;(4f)^{1-13}(5d)^{0-1}(7S)^2 \\ (c)\;(5f)^{1-14}(6d)^{0-1}(7s)^2 \\ (d)\;(5f)^{0-1}(6d)^{1-14}(7s)^2$

Solution :
The elements in which the last electron enters one of the 5f-orbitals are called 4f-block elements or second inner transition series
They are also called Actinides because they come immediately after actinium.
The general electronic configuration is
$(5f)^{1-14}(6d)^{0-1}(7s)^2$ is correct answer.
$[Rn]5f^{1-14} 6d^{0-1} 7s^2 Id$
Hence c is the correct answer.
edited Sep 25, 2017 by meena.p