In municipal sewage,$BOD$ values (in $ppm$) are

Identify the correct statements from the following:
$a$) $BOD$ value of clean water is less than $5 \ ppm$
$b$) Oxidation of ethene in the presence of $Pd^{2+}$ catalyst in aqueous medium gives acetic acid
$c$) Photochemical smog causes damage to plant life
$d$) Reducing smog is a mixture of smoke,fog and $SO_2$

Which of the following is a major air pollutant?

The acid that is believed to be mainly responsible for the damage of the Taj Mahal is ...

Which of the following statement$(s)$ is/are incorrect:

Which of the following is harmful to calcium-containing structures and is responsible for causing cough and throat irritation in humans?