Explain the following :
a. Oil paintings trun blackish after sometime . What is the salt formed ? Assume oil painsts contian leas .
b. While testing oxalate ion . Gas obtained burns with a blue flame initally but is put off instantly even as fas appears coming .

Explanation

Oil paintings turen blackish after some time due to formation of elad sub phide on its suface .
`Pb^(2+) + underset ((air)) (S^(2-)) rarr underset (Black) (Pbsnarr)`
b.`underset (acid) underset ("Oxalic") (H2C_2O_4) overset (Delta) (rarr) underset ("mmnoxide") underset ("Carbon") (COuarr) + underset ("dioxide") underset ("Carbon") (CO_2uarr) + H_2O`
`CO` burns with a blue filame. It diffuses faster than `CO_2` Once `CO` burns with a blue flame it is put off by `CO_2` which diffuses later .