The correct answer is option 1: a shower of raindrops.

When light from the Sun passes through a raindrop, it undergoes a process called refraction. Refraction is the bending of light as it passes from one medium to another, such as from air to water. Each raindrop acts like a tiny prism, splitting the white light from the Sun into its component colors. This is the basis for the formation of a rainbow.

So, when light passes through many raindrops in the atmosphere, it gets scattered in different directions, spreading the light energy across a wider area. This is why we see sunlight spreading out and illuminating the sky during or after rain.

Although the other options also involve the manipulation of light, they do not specifically describe the spreading of sunlight as mentioned in the question. A plane mirror would reflect light, but it does not change the spread of light. A convex lens or a combination of convex and concave lenses can focus or diverge light, but they do not spread sunlight in the same way that raindrops do.

In conclusion, a shower of raindrops is the correct answer as it scatters light and spreads sunlight.