On increasing temperature, solids are converted to _____.

When a solid is heated, the particles are given more energy and start to vibrate faster. 

At a certain temperature, the particles vibrate so much that their ordered structure breaks down. At this point, the solid melts into liquid.

The temperature at which this change from solid to liquid happens is called the melting point. Each solid has a set melting point at normal air pressure.

Hence option B is correct