Which of the following pair of ores cannot be converted into corresponding metals by pyrometallurgy?

If a normal chord at a point $t$ on the parabola $y^2=4ax$ subtends a right angle at the vertex,then $t^2$ equals to

Which structure acts as the pacemaker of the heart?

The work done in increasing the size of a rectangular soap film from $10 \, cm \times 6 \, cm$ to $10 \, cm \times 11 \, cm$ is $3 \times 10^{-4} \, J$. The surface tension of the film is:

Assertion : Replication and transcription occur in the nucleus but translation takes place in the cytoplasm.
Reason : $mRNA$ is transferred from the nucleus into the cytoplasm where ribosomes and amino acids are available for protein synthesis.

The major product obtained on interaction of phenol with sodium hydroxide and carbon dioxide is