What type of solid is silica?

The conductivity of semiconductors $..........$ with an increase in temperature.

How many of the following compounds show ferrimagnetism?
$Fe_3O_4; MgFe_2O_4; NiFe_2O_4; MnO; CrO_2$

Among solids,the highest melting point is established by

Heating steel to bright redness and then cooling suddenly by plunging it into oil or water,makes it

Given below are two statements.
Statement $I$ : $O_2, Cu^{2+}$ and $Fe^{3+}$ are weakly attracted by magnetic field and are magnetized in the same direction as magnetic field.
Statement $II$ : $NaCl$ and $H_2O$ are weakly magnetized in opposite direction to magnetic field.
In the light of the above statements,choose the most appropriate answer from the options given below: