2. Classify the following elements into \( 1^{\text {st }}, 2^{\text {nd }}, 3^{\text {rd }} \) and \( 4^{\text {th }} \) series.
\( Cr , Mt \), Tc, Os, Mo
(1) \( 1^{\text {st }} \) series \( - Cr ; 2^{\text {nd }} \) series \( - Tc , Mo ; 3^{\text {rd }} \) series - Os; \( 4^{\text {th }} \) series - Mt
(2) \( 1^{\text {st }} \) series - Tc, Mo; \( 2^{\text {nd }} \) series - Os; \( 3^{\text {rd }} \) series - \( Mt ; 4^{\text {th }} \) series \( - Cr \)
(3) \( 1^{\text {st }} \) series \( - Tc , Mo ; 2^{\text {nd }} \) series \( - Mt ; 3^{\text {rd }} \) series - \( Cr ; 4^{\text {th }} \) series - Os.
(4) \( 1^{\text {st }} \) series \( -O Os ; 2^{\text {nd }} \) series \( - Tc ; 3^{\text {rd }} \) series Mt, Mo; \( 4^{\text {th }} \) series \( - Cr \)
