According to the Solow model, which type of government spending is more likely to raise the long-term growth rate of output per person, spending on infrastructure or spending on research and development?

What will be an ideal response?

Spending on research and development. As a production input, infrastructure is much like capital, subject to diminishing returns. Infrastructure investments are likely to raise the level of output per person, but any effect on the growth rate is likely to be temporary. Spending on research and development, when effective, raises productivity directly. There are no diminishing returns, and improvements in technology may stimulate and enable further improvements, including those funded by private businesses.