Long term capital Gain tax saving doubt

If  Long term gain from Stocks/House sale is reinvested as new house/land/stocks then entire gain wont be taxable ? Please guide

if it is bought at 2020  and LT gain received in 2021 then can I use last year property/stocks that purchased to mitigate gain of next year 2021 

or

if it is bought at 2022  and LT gain received in 2021 then can I use 2022 year property/stocks that purchased to mitigate gain of year 2021