No, it is not safe.

If the parent page is not secured with https then there is no guarantee that the user will see the correct https iframe URL.

An attacker may perform a man-in-the-middle attack on the parent page and cause it to render an iframe to the attacker's website. Since browsers do not indicate the url or https status of iframes the user would be none the wiser they are communicating with someone fraudulent.

No, it is not safe.

If the parent page is not secured with https then there is no guarantee that the user will see the correct https iframe url.

An attacker may perform a man-in-the-middle attack on the parent page and cause it to render an iframe to the attacker's website. Since browsers do not indicate the url or https status of iframes the user would be none the wiser they are communicating with someone fraudulent.

No, it is not safe.

If the parent page is not secured with HTTPS, there is no guarantee that the user will see the correct HTTPS iframe URL.

An attacker may perform a man-in-the-middle attack on the parent page and cause it to render an iframe to the attacker's website. Since browsers do not indicate the URL (or HTTPS status) of iframes the user would be none the wiser they are communicating with someone they are not intending to.

No, it is not safe.

If the parent page is not secured with https then there is no guarantee that the user will see the correct https iframe URL.

An attacker may perform a man-in-the-middle attack on the parent page and cause it to render an iframe to the attacker's website. Since browsers do not indicate the url or https status of iframes the user would be none the wiser they are communicating with someone fraudulent.