You are a portfolio manager and using CAPM for making recommendations to your clients. Security research department has developed the following information:

$\backslash$table$[[,$E$($R$),$SD$,$Beta$],[$Infosys$,14\%,15\%,0\mathrm{.}8],[$SBI$,17\%,12\%,1\mathrm{.}5],[$S&P CNX Nifty,$14\%,10\%,1],[$T$/$B$,5\%,0,0]]$

Identify and justify which stock would be more appropriate for an investor who wants to

$($i$)$ add this stock to a well$-$diversified portfolio.

$($ii$)$ hold this stock as single stock portfolio.