Which of the following is a common on-page SEO technique?

Optimizing title tags and meta descriptions is a fundamental on-page SEO technique because it directly influences how search engines interpret the content of a webpage and how users perceive it in search results. Title tags help define the title of a webpage, showing up as the clickable link in search engine results, while meta descriptions provide a brief summary of the page's content, encouraging users to click through. Properly optimized title tags and meta descriptions can significantly improve a webpage's visibility and click-through rate, as they align both with search engine algorithms and user intent.

In contrast, other options focus on off-page strategies or different forms of marketing. Building backlinks, while crucial for enhancing a site's authority and search ranking, is considered an off-page SEO strategy. Creating ads on social media and initiating email marketing campaigns pertain to paid advertising and direct marketing efforts, which do not fall under the scope of on-page SEO. These strategies may complement an overall digital marketing strategy but do not involve direct adjustments to the content or structure of a webpage itself.