The correct answer for why wind is often found to blow on a hot summer day is option 3: convection current of air.

Convection refers to the process of heat transfer through the movement of a fluid, such as air. On a hot summer day, the sun heats up the surface of the Earth, including the air in contact with it. Hot air has lower density compared to the cold air, which causes it to rise. As the hot air rises, it creates an area of lower pressure near the surface.

In response to the pressure difference, cooler air from the surrounding areas flows in to fill the void, creating air movement or wind. This movement of air due to the difference in temperature is known as convection.

Options 1 and 2, conduction of heat between air and soil on the Earth and radiation from the soil, are not the primary reasons why wind is observed on a hot summer day. While these processes do contribute to the overall temperature gradient, it is the convection process that primarily drives the movement of air and the resulting wind.

The fourth option, None of the above, is incorrect as option 3, convection current of air, is the correct explanation for wind on a hot summer day.