Naturgy is a large, stable regulated/contracted energy utility with significant asset intensity and predictable operating cash flows, which can make some hybrid capital useful. In 2022 it generated strong EBITDA of €4.954bn and operating cash flow of €4.242bn, while net debt-like financial liabilities were substantial: noncurrent financial liabilities of €13.999bn plus current financial liabilities of €2.302bn, partly offset by €3.985bn cash.

Key considerations for hybrid-bond reliance:

- **Leverage is material but manageable.** Gross financial liabilities were about €16.3bn versus EBITDA of about €5.0bn, and cash was high. Equity was €10.0bn, so the balance sheet has a reasonable equity cushion.
- **Interest coverage weakened but remains acceptable.** Finance costs rose to €837m in 2022, implying EBITDA/finance cost around 5.9x and operating profit/finance cost around 3.7x. This supports some subordinated/hybrid issuance but does not argue for very heavy reliance.
- **Rate environment became much less favorable.** Euro swap rates increased sharply in 2022, and non-financial investment-grade spreads also rose. Hybrids would be meaningfully more expensive than senior debt, so excessive reliance would raise funding costs.
- **Hybrids can help protect credit metrics.** For a utility with large investment needs and dividend distributions, hybrids may provide partial equity credit from rating agencies while avoiding common-equity dilution.
- **But 75% or 100% would be too aggressive.** Hybrids are subordinated, callable, coupon-deferrable instruments and should complement, not replace, senior debt and common equity. Overreliance could increase refinancing and investor-perception risk.
- **0% is also too conservative.** Given Naturgy’s scale, regulated asset base, and need to maintain credit metrics during investment and volatile energy-market conditions, some hybrid capital is useful.

Overall, hybrid bonds should be a **meaningful but minority component** of the capital structure. Among the choices, **25%** best balances credit-support benefits against higher cost and subordination risk.

<answer>25%</answer>